I've made a little progress with this - it seems that when a NVarChar parameter is passed in the length of that parameter fixes the maximum length of the parameter....

I'm still getting this error. We're using SQL Dependency to cache some pretty straightfoward queries:

SELECT [t0].[AgentID] AS [AgentCode], [t1].[AgentID] AS [AgentGroupCode], UPPER([t0].[AgentName]) AS [AgentName], [t0].[AffiliateID] AS [affiliateId], [t0].[CashBackAgent] AS [IsCashbackAgent],...