Odd error in email.

Our site has been online for a year. We have made no changes recently.
Yesterday we started getting errors when reading email. Stack overflow line: xxxx. Also, we are unable to reply to any email.
Any ideas what may be causing this?
We contacted our server, they seem to think it's a programming issue.

Do you mean the internal mail inside Dolphin like from user to user?

Yes, the internal mail.

Never heard of this happening before... Do you have a lot of emails in your inbox or is the one you're trying to read really large? The stack overflow is usually because memory is exhausted and I can't think of how that could happen unless it's trying to load a lot of mail. 

That was our first thought too. We deleted all email except one and it's a small one.
  All members are having this issue though... We are mind boggled.

What code is on the line number from the error message?

The error munber changed each time.
 Odd thing is... It's working this morning. I do hope this doesn't happen again. Non-working email makes some very unhappy members.

Well, that ws dhort lived. It's doing the same thing again.

The error is consistent now though.

Stack overflow at line 1689

We have rebooted the server and loaded a good copy of mail.php, no change. We still get the same error and can not reply to mail.
 Another thing... occasionally the page shows a jumbled up.

A new update, it will work in firefox now, but still no go in explorer.

I'm experiencing the same 'Stack overflow..' issue on some PCs, could some one please provide a solution? The error is there on some PCs where Internet Explorer version 8 is used (on Windows XP), but also when Firefox is used. The only browser that those PCs don't seem to experience the error is Google Chrome.

hi all, just to let you know that it seems to be fixed now on our site. it's been fixed by 1 of our other add on providers and they said they have made the required changes in 1 of their files (comet.js).  thank you very much webmasterff and alex and all others !