Can you check your PHP session settings are correct?

When you load the form to submit a new bug, MantisBT generates a nonce (random characters), remembers it within the PHP session and then embeds the nonce into the form. When you go to submit the form, MantisBT confirms that the nonce embedded into the form matches what it can find in the current PHP session.

So if your PHP sessions expire too quickly, MantisBT won't be able to confirm that the nonce is valid.

I am new to Mantis and PHP so I don't know which PHP session settings to check and what would be correct settings for them. A little guidance would be useful.

I have increased session.gc_maxlifetime as suggested in issue 0011680 and will see if this makes any difference.

We have now run it for the best part of a day with the increased value and so far have not had any re-occurrences.