There is a hard limit of the number of parameters any single SQL statement can have, and that is 2100 (for SQL Server 2005), or 1024 (for SQL Server 2000).
Does anyone know of a way to increase that number?
If you'd like to know "why" (as I would be dying of curiosity myself), the ansewr is in this:
MyL2SDataContext.Accounts.Where(acct=> selectedAccountIDs.Contains(acct.ID))...
Thanks,