Ah, I see. Thanks!

I answered my own question. I found it's a browser issue - user was using Chrome, which apparently is a problem. Firefox doesn't have this problem.

Thanks, adding the MaxHttpCollectionKeys key to web.config fixed the issue.

No, it doesn't fix the problem, but at least I know what's causing the problem!
Yes, my sp does accept multi-value parameters. The SP isn't getting run.

I found...

A-ha. I googled ThrowIfMaxHttpCollectionKeysExceeded() and saw what some others have found. I have parameters which - if the user 'selects all' - results in lots of parameters. When I re-ran...

Got the log files - I see this in several places. I don't know what it means, but it seems to correspond with every time I tried to run the...

The report is also deployed to a dev server where it works fine - it is firing the stored procedure on the dev server as well.
Is there some setting...