Not sure what the cause is but i have repeated trouble with Tokens expiring when using the PM system.
I will set up and type a new message, get all the way to the end and then come to post it and it says token expired and wipes my message.
Recently I started typing my messages in word and then cut and paste to get them to go without loosing your thoughts each time and having to retype.
I have had this issue with posts as well when attaching pictures.
Its very frustrating and now and then i fortget to use word like i just did and lost the whole thought process etc in the pm i was sending.
I regularly clear my browser etc and re log in so any other help would be appreciated.