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>