I am getting a similar result. As soon as I open a spark file and attempt to invoke the intellisense the extension crashes. After reviewing the log file, I found the following exception:
System.ArgumentNullException: Value cannot be null.
Parameter name: oldValue
 at System.String.Replace(String oldValue, String newValue)
 at SparkSense.Parsing.ProjectExplorer.GetCurrentViewPath()
 at SparkSense.Parsing.ViewExplorer.InitCurrentView()
 at SparkSense.Parsing.ViewExplorer..ctor(IProjectExplorer projectExplorer)
 at SparkSense.StatementCompletion.CompletionSource..ctor(ITextBuffer textBuffer, IProjectExplorer projectExplorer)
 at SparkSense.StatementCompletion.CompletionListener.TryCreateCompletionSource(ITextBuffer textBuffer)
 at Microsoft.VisualStudio.Language.Intellisense.Implementation.CompletionBroker.<>c__DisplayClass1.<CreateSourcesForBuffer>b__0(ICompletionSourceProvider provider)
 at Microsoft.VisualStudio.Text.Utilities.GuardedOperations.InvokeMatchingFactories[TExtensionInstance,TExtensionFactory,TMetadataV
iew](IEnumerable`1 lazyFactories, Func`2 getter, IContentType dataContentType, Object errorSource)
I've fixed the bug in my local build for the original issue. This will be released soon, but you can get it from source if you're desperate. @Rohland, I don't think yours is the same issue, it's happening in an entirely different area of the code and I think it might be because you don't have your views in a "Views" folder in the solution. Just guessing, but I'll look into it anyway, I don't want the exception thrown, I'd rather have the IntelliSense just *not* work.
I had this problem - I fixed it by doing the following:
Go through each View folder in the solution and check that Studio hasn't added the same spark file twice to the solution. In my case, it had doubled up a file called details.spark. The solution would compile fine, but the sparksense threw the error.
I just realised that I attempted to use the plugin on a webforms project that was recently integrated with MVC. There was a 'Views' folder but I noticed that the folder name was all lowercase. I haven't re-attempted to use the plugin on this specific project, but that may be the issue.