Why does xCode crash when I open a project?

I'm trying to open a project with the latest version of xCode (updated today). For some reason, it crashes. I can't open any project, it crashes all times :( Have you experienced anything similar to this? I've looked at many similar questions, but none of them helped. Crash report begins like this (if helps):

Process:         Xcode [1631]
Path:            /Applications/Xcode.app/Contents/MacOS/Xcode
Identifier:      com.apple.dt.Xcode
Version:         5.0.2 (3335.32)
Build Info:      IDEApplication-3335032000000000~4
App Item ID:     497799835
App External ID: 106632651
Code Type:       X86-64 (Native)
Parent Process:  launchd [133]
Responsible:     Xcode [1631]
User ID:         501

Date/Time:       2013-11-12 18:14:14.782 +0100
OS Version:      Mac OS X 10.9 (13A603)
Report Version:  11
Anonymous UUID:  041E96A2-1123-3287-3FF6-A3F30382FC69

Sleep/Wake UUID: C6807823-3147-4602-B01F-A2A9E80B8259

Crashed Thread:  0  Dispatch queue: com.apple.main-thread

Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000

Application Specific Information:
ProductBuildVersion: 5A3005
ASSERTION FAILURE in /SourceCache/DVTFoundation/DVTFoundation-3542/Framework/Classes/FileTypes/DVTFileDataType.m:616
Details:  stringRep should be a non-empty string, but it is nil
Object:   <DVTFileDataType>
Method:   +fileDataTypeFromStringRepresentation:
Thread:   <NSThread: 0x7fc7d9d151c0>{name = (null), num = 1}
Hints:   None
Backtrace:
  0  0x0000000102e69ea8 -[IDEAssertionHandler handleFailureInMethod:object:fileName:lineNumber:messageFormat:arguments:] (in IDEKit)
  1  0x0000000101bf17a5 _DVTAssertionHandler (in DVTFoundation)
  2  0x0000000101bf1ad4 _DVTAssertionFailureHandler (in DVTFoundation)
  3  0x0000000101b8ca94 +[DVTFileDataType fileDataTypeFromStringRepresentation:] (in DVTFoundation)
  4  0x0000000107fa5dd0 -[Xcode3TargetProduct fileDataType] (in DevToolsCore)
  5  0x00000001025f25ce -[IDEBuildableProductRunnable runnableUTIType:] (in IDEFoundation)
  6  0x00000001025ee340 -[IDEProfileSchemeAction _updateAnalysisToolService] (in IDEFoundation)
  7  0x0000000101c02bc8 __73-[DVTObservingBlockToken observeValueForKeyPath:ofObject:change:context:]_block_invoke (in DVTFoundation)
  8  0x0000000101c19e88 DVTInvokeWithStrongOwnership (in DVTFoundation)
  9  0x0000000101b58479 -[DVTObservingBlockToken observeValueForKeyPath:ofObject:change:context:] (in DVTFoundation)
 10  0x00007fff90c4bc18 NSKeyValueNotifyObserver (in Foundation)
 11  0x00007fff90c4ade8 NSKeyValueDidChange (in Foundation)
 12  0x00007fff90c4fa56 -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] (in Foundation)
 13  0x0000000102f6b395 -[IDEContextAutocreationController addBuildable:toScheme:] (in IDEKit)
 14  0x0000000102f6bd68 -[IDEContextAutocreationController createSchemeForBuildable:withName:] (in IDEKit)
 15  0x0000000102f6b16d -[IDEContextAutocreationController createDefaultSchemeForBuildable:] (in IDEKit)
 16  0x0000000102cf2976 -[IDEContextAutocreationController autocreateSchemesForcingAutocreate:] (in IDEKit)
 17  0x0000000101c03618 -[NSObject(DVTObservingConvenience) _dvt_newObserverForKeyPath:options:owner:withHandlerBlock:] (in DVTFoundation)
 18  0x0000000101b57fc5 -[NSObject(DVTObservingConvenience) dvt_newObserverForKeyPath:options:owner:withHandlerBlock:] (in DVTFoundation)
 19  0x0000000101c0326c -[NSObject(DVTObservingConvenience) dvt_addObserverForKeyPath:options:owner:withHandlerBlock:] (in DVTFoundation)
 20  0x0000000102f6a11e __53-[IDEContextAutocreationController initForWorkspace:]_block_invoke_2 (in IDEKit)
 21  0x0000000101c03618 -[NSObject(DVTObservingConvenience) _dvt_newObserverForKeyPath:options:owner:withHandlerBlock:] (in DVTFoundation)
 22  0x0000000101b57fc5 -[NSObject(DVTObservingConvenience) dvt_newObserverForKeyPath:options:owner:withHandlerBlock:] (in DVTFoundation)
 23  0x0000000101c0326c -[NSObject(DVTObservingConvenience) dvt_addObserverForKeyPath:options:owner:withHandlerBlock:] (in DVTFoundation)
 24  0x0000000102f69e8b __53-[IDEContextAutocreationController initForWorkspace:]_block_invoke (in IDEKit)
 25  0x0000000101c02bc8 __73-[DVTObservingBlockToken observeValueForKeyPath:ofObject:change:context:]_block_invoke (in DVTFoundation)
 26  0x0000000101c19e88 DVTInvokeWithStrongOwnership (in DVTFoundation)
 27  0x0000000101b58479 -[DVTObservingBlockToken observeValueForKeyPath:ofObject:change:context:] (in DVTFoundation)
 28  0x00007fff90c4bc18 NSKeyValueNotifyObserver (in Foundation)
 29  0x00007fff90c4ade8 NSKeyValueDidChange (in Foundation)
 30  0x00007fff90c4fa56 -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] (in Foundation)
 31  0x000000010268481a __81-[IDEWorkspace _finishLoadingAsynchronously:shouldUpgradeFromSimpleFilesFocused:]_block_invoke (in IDEFoundation)
 32  0x0000000102684ac1 __81-[IDEWorkspace _finishLoadingAsynchronously:shouldUpgradeFromSimpleFilesFocused:]_block_invoke281 (in IDEFoundation)
 33  0x00007fff90c6b055 -[NSBlockOperation main] (in Foundation)
 34  0x00007fff90c4a591 -[__NSOperationInternal _start:] (in Foundation)
 35  0x00007fff90c4a23b __NSOQSchedule_f (in Foundation)
 36  0x00007fff852dc2ad _dispatch_client_callout (in libdispatch.dylib)
 37  0x00007fff852e3f03 _dispatch_main_queue_callback_4CF (in libdispatch.dylib)
 38  0x00007fff859b9839 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ (in CoreFoundation)
 39  0x00007fff85974b14 __CFRunLoopRun (in CoreFoundation)
 40  0x00007fff85974275 CFRunLoopRunSpecific (in CoreFoundation)
 41  0x00007fff8bc2ef0d RunCurrentEventLoopInMode (in HIToolbox)
 42  0x00007fff8bc2ecb7 ReceiveNextEventCommon (in HIToolbox)
 43  0x00007fff8bc2eabc _BlockUntilNextEventMatchingListInModeWithFilter (in HIToolbox)
 44  0x00007fff8b0af28e _DPSNextEvent (in AppKit)
 45  0x00007fff8b0ae8db -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] (in AppKit)
 46  0x00007fff8b0a29cc -[NSApplication run] (in AppKit)
 47  0x00007fff8b08d803 NSApplicationMain (in AppKit)
 48  0x00007fff899005fd start (in libdyld.dylib)

Thanks in advance!

The most common cause of these kinds of crashes is a corrupted DerivedData directory. You can delete this directory (and many of us do this regularly, just to keep things more stable).

Open Xcode
Preferences
Locations
The Derived Data option will tell you where your directory is
Delete that directory
Try to open your project

Personally, I select "Custom" for Derived Data, and put it in /tmp/xcode-build. This deletes the directory every time I reboot, and is easier to type than the default when I want to delete it by hand.

EDIT: One more common problem: you often need to reboot after upgrading Xcode. Since Xcode 5, that's been less of an issue, but it's still worth trying, especially if you're upgrading from Xcode 4.