Problems uploading photos??

[EMT/FF99]

I received the following message this evening while trying to upload some photos:

Your submission could not be processed because a security token was missing or mismatched.

If this occurred unexpectedly, please inform the administrator and describe the action you performed before you received this error.

[EMT/FF99]

When I try to upload photos, I get the "sending request to thewatchdesk.com" at the bottom of the attachment page. If I am able to get 1 photo possibily uploaded I then get a message stating the upload failed. Any idea to what is going on??
Never had a problem in uploading photos, sizes are within the required parameters too.

[regs1]

I have to check why, it this problem reappears once in a while for different reasons

[EMT/FF99]

No problem at all.