Unintuitive exception thrown for Excel 5.0/95 format worksheets

Steps to Reproduce:
1. Save an Excel worksheet using the format Microsoft Excel 5.0/95
2. Provide the path to that worksheet to DataSetHelper.CreateDataSet()
3. An ArgumentNullException is thrown from System.IO.MemoryStream.

There isn't much reason for excellibrary to support such an old format, but a 
better error message might be useful. Is it possible to determine whether the 
file is in the correct format? If so, perhaps the code could throw some more 
specific Exception?

I'm using code checked out from the current trunk (r53).

Full StackTrace:
   at System.IO.MemoryStream..ctor(Byte[] buffer, Boolean writable)
   at System.IO.MemoryStream..ctor(Byte[] buffer)
   at ExcelLibrary.SpreadSheet.Workbook.Load(Stream stream)
   at ExcelLibrary.SpreadSheet.Workbook.Load(String file)
   at ExcelLibrary.DataSetHelper.CreateDataSet(String filePath)
   at TestExcelImport.Program.Main(String[] args) in c:\users\theuser\documents\visual studio 2010\Projects\TestExcelImport\TestExcelImport\Program.cs:line 12
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

Original issue reported on code.google.com by etkl...@gmail.com on 2 Jun 2011 at 6:28

tgui78 / excellibrary

Unintuitive exception thrown for Excel 5.0/95 format worksheets #94