Security Implications of turning off the "Disallowed Characters" test?

[eluser]Rob Howard[/eluser]
Hi guys, thanks for all your help and a wonderful framework in CodeIgniter.

A project that had been live for 2+ years recently started throwing a "URI has disallowed characters" error for every URL, none of which had strange or unusual characters in them as far as I could tell. I am not aware of any changes that took place on the server to cause this. To fix the problem for the time being, I've simply commented out the line of code that throws the error, effectively turning off this "disallowed characters" test.

I have seen statements that this opens up potential security issues. Could you please elaborate on what the potential security problems are, so that I can make my client aware of them and allow them to make an informed decision on how to proceed?

Thanks!