SSRS Report Continues running after SPROC throws an error - how to stop?

Here is the scenario:

I have a shared dataset based upon a stored procedure that has validation like this:

if @pAssetFlag = 1 and @pDriverGroupKeys <> N'0'
begin
raiserror(' >>> P L E A S E  N O T E - IF THE ASSET VIEW IS SELECTED.. blah blah blah',16,1)
return -1
end

On my development server that has "enable remote errors" turned off in the SSRS config, if I run the report and pass in an invalid parameter combination, I get an error back immediately like this:

• An error has occurred during report processing. (rsProcessingAborted)
  • Query execution failed for dataset 'dsValidateDashboardParameters'. (rsErrorExecutingCommand)
    • For more information about this error navigate to the report server on the local server machine, or enable remote errors

The good thing about that is it errors out immediately, the bad thing is it isn't returning the error message I'd like the user to see.

On the production server with remote errors enabled, it returns this message:

• An error has occurred during report processing. (rsProcessingAborted)
  • Query execution failed for dataset 'dsValidateDashboardParameters'. (rsErrorExecutingCommand)
    •  >>> P L E A S E  N O T E - IF THE ASSET VIEW IS SELECTED.. blah blah blah

This is great except that it takes 90 seconds before the message appears.  A look at the execution log indicates it spent 30 seconds on data retrieval then 60 seconds on report processing before the error was thrown.

Does anyone know how to configure SSRS so it throws the error message immediately with remote errors enabled?

Thanks for any insight.