Unhandled exception

I write a function/method to accept four paramater. function signature is  

public char change(char paragraph,char changeletter, char startpoint,char endginpoint)

SharpDeveloper crashed when i wrote

utility.switcher.change(message[i], chletter, '

1. Utility is the namespace name
2. Switcher us the class name
3. change is the function/method name
4. i is the index variable
   

I did  write the line before in code same error was occure. Somehow continue option worked. Second time when i wrote the line error occured and know it won't work.

The error message that popup is

SharpDevelop Version : 5.1.0.5216-0e58df71
.NET Version         : 4.7.02053
OS Version           : Microsoft Windows NT 6.3.9600.0
Current culture      : English (United States) (en-US)
Running under WOW6432, processor architecture: x86-64
Working Set Memory   : 130456kb
GC Heap Memory       : 20314kb

Exception thrown:
System.OverflowException: Arithmetic operation resulted in an overflow.
   at ICSharpCode.AvalonEdit.Utils.CharRope.ToString(Rope`1 rope, Int32 startIndex, Int32 length)
   at ICSharpCode.AvalonEdit.Document.RopeTextSource.GetText(Int32 offset, Int32 length)
   at ICSharpCode.NRefactory.Editor.ReadOnlyDocument.GetText(Int32 offset, Int32 length)
   at CSharpBinding.Parser.TParser.AddCommentTags(SyntaxTree cu, IList`1 tagComments, ITextSource fileContent, FileName fileName, IDocument& document)
   at CSharpBinding.Parser.TParser.Parse(FileName fileName, ITextSource fileContent, Boolean fullParseInformationRequested, IProject parentProject, CancellationToken cancellationToken)

Now the solution will open but the source file which contain the code will not open.