I have been using VS2010 for a few weeks but for the past few days it has been totally unusable, when i type anything into the editor Visual Studio throws an exception, then I get lots of intellisence errors (the code is fine, I can compile it if I run before trying to use the editor) - here is the log message:
<entry>
<record>241</record>
<time>2011/01/25 08:30:34.109</time>
<type>Error</type>
<source>Editor or Editor Extension</source>
<description>System.InvalidCastException: Unable to cast COM object of type 'System.__ComObject' to interface type 'Microsoft.VisualStudio.TextManager.Interop.IVsTextReplaceEvents'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{CF9928D9-65AE-4319-A446-94ED5C45ECDE}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).
 at System.StubHelpers.StubHelpers.GetCOMIPFromRCW(Object objSrc, IntPtr pCPCMD, Boolean& pfNeedsRelease)
 at Microsoft.VisualStudio.TextManager.Interop.IVsTextReplaceEvents.OnReplace(ChangeInput[] pCI)
 at Microsoft.VisualStudio.Editor.Implementation.VsTextBufferAdapter.OnTextBufferChangedHighPriority(Object sender, TextContentChangedEventArgs e)
 at Microsoft.VisualStudio.Text.Utilities.GuardedOperations.RaiseEvent[TArgs](Object sender, EventHandler`1 eventHandlers, TArgs args)</description>
</entry>
<entry>
<record>242</record>
<time>2011/01/25 08:30:34.125</time>
<type>Error</type>
<source>Editor or Editor Extension</source>
<description>System.InvalidCastException: Unable to cast COM object of type 'System.__ComObject' to interface type 'Microsoft.VisualStudio.Editor.Implementation.IVsTextStreamEvents_Private'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{96FC7D44-BCDD-4F00-AE4D-07E26B2C0E52}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).
 at System.StubHelpers.StubHelpers.GetCOMIPFromRCW(Object objSrc, IntPtr pCPCMD, Boolean& pfNeedsRelease)
 at Microsoft.VisualStudio.Editor.Implementation.IVsTextStreamEvents_Private.OnChangeStreamText(Int32 iPos, Int32 iOldLen, Int32 iNewLen, Int32 fLast)
 at Microsoft.VisualStudio.Editor.Implementation.VsTextBufferAdapter.OnTextBufferChanged(Object sender, TextContentChangedEventArgs e)
 at Microsoft.VisualStudio.Text.Utilities.GuardedOperations.RaiseEvent[TArgs](Object sender, EventHandler`1 eventHandlers, TArgs args)</description>
</entry>
Looks like a problem with an extension or add in. Disable them all then re-enable one by one and see if one of them is acting up..
This seems like it might be due to some info missing from the registry on your computer. If you go to the MS Connect website you'll find a discussion about this issue and what seems to be a solution as well.
Solution (copied from that page):
Using regedit look at the following key:
On 32-Bit Windows:
[HKEY_CLASSES_ROOT\CLSID\{73B7DC00-F498-4ABD-AB79-D07AFD52F395}\InProcServer32]
On 64-Bit Windows:
[HKEY_CLASSES_ROOT\Wow6432Node\CLSID\{73B7DC00-F498-4ABD-AB79-D07AFD52F395}\InProcServer32]
The "(Default)" value should be one of the following:
On 32-Bit Windows:
"C:\Program Files\Common Files\Microsoft Shared\MSEnv\TextMgrP.dll"
On 64-Bit Windows:
"C:\Program Files (x86)\Common Files\Microsoft Shared\MSEnv\TextMgrP.dll"