So after reviewing this again, I think SSRS is converting the data source to ntext because it's so large, and then obviously when passing into the procedure, it blows up.

Even though the source column is VARCHAR in my dataset, I tried adding a cast AS VARCHAR, and I'm still having the same error.

Obviously If I was SQL2005/8 I could use (MAX), but for now I'm stuck. Any thoughts at all would be most appreciated.