error when attaching pdf to post
 

i am attempting to attach a 9.5mb pdf to a post.

the 'manage attachments' pop-up window shows the progress of the upload (chrome) after i select the file and click 'Upload' but when it reaches 100% the window displays the following text:

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

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