Hi rpike,
- What does "failing" mean?
- What does the log contain?
- Have you tried to test your theory about size limitation?
- What does the CGI documentation say about limitations on the redirect URL?
- How do you "tack on" the extra parameter (show the code)?
- What is the resulting URL?
- What happens when you request that URL directly with a client?
Those are some examples of information that would be useful for anyone trying to assist you.
The way forward always starts with a minimal test.