Private messages not sending

Hey everyone, ive had a few members contact me over the past few months telling me their private messages arent sending all the time, I myself have not had any problems with it, but i rarely use it. The members that seem to be having issues are very active on the forum and seem to send out alot of messages, im not sure how to help them, but since im the admin, they come to me. And im not even sure how they know they are not sending. Ive had a member send me a screen shot of his outbox but i see nothing wrong with it, but ill attach it anyway because maybe im over looking something.

Have you asked the members who was to received the pm's if they have received them?

The last complainant said he sent me a pm but i never received it so he had to email me instead. It seems to be an intermittent issue.

Please post this information:

Code:

[b]Forum Link:[/b]
[b]Forum Version:[/b]
[b]Was anything modified before this happened:[/b]
[b]Is the inbox full:[/b]

http://www.gmbbodyforum.com/
Invision is the version
Only thing modified was the forum skin but this was months ago before and after complaints
And no the inbox is not full

Did the members who have complained get any kind of message when they pressed the send button?

ACP > General > Message & Email (Private Messages)

No there was no error message or anything, and thanks erchima but ive already done all that. Honestly i dont think its a big deal, and i think we can "solve" this topic. Like i said, it seems to be an intermittent issue, but nothing ive experienced. Ill send them a pm and do some testing of my own. I just wanted to bring the question here to see if this may have been a common problem. Thanks all

So you want to lock this topic?

yes