I don't know if this will fix the problem, but you could change:

Where ( OITDate >=(@StartDate)) And ( OITDate <=(@EndDate))

to

Where OITDate between @StartDate And @EndDate

The error sounds like one...

I do something similar to this with support 'cases', but I use another report to show the details of the case, instead of a sub-report, and link to it using...