Sometimes, actually quite often, when I send an email (POP account) from my Nokia 8800, I get the message "String index out of range:-1". There is a red flashing stop sign too.
I only get this message when sending an email from the phone. Sometimes it works, many times I get this message. It is not a network problem because I sometimes get this message when simply trying to save an email to send later.
I have had other Nokia phones with POP email clients and their software is buggy at best. I use Profimail on my N70 and it is awesome.