checkAction() fatal error. Unknown action ID: 1

I get a blank page and this error message when attempting to view a private message in 7.2.1.

checkAction() fatal error. Unknown action ID: 1

This is being caused by the "mail box" block.  However, I have to have this block to read the message. Removing it will load the page. See the screen shot.

** Not Solved ***

Sorry to take up forum space but for the archiving purpose and as always to possibly help someone else here is the problem.

By default after upgrade the "mail box" block was enabled for both guest and member.  Guest access is not possible here.  Unchecking visible to guests fixed this problem for myself only.  Only problem now is that all messages from other people other than  myself are not working.

EDIT UPDATE:  Only messages to myself are viewable. Messages from other members continue to give the error message. Other members are getting the same thing.

Ok I've test several different scenarios.  As long as the "mail box" block exist this error arrives.  You can remove visibility for members and guest and leave the block in place and the error goes away but then you have no mail box.

I'm hurting for help on this.  I appreciate everyone always. Seems tough latley to draw attention to individual problems without a ticket. Anybody that might have an idea on this I am always grateful.  I'm stuck on this one.

If you wish, you can PM me the site login and FTp details and I will investigate and tell you what is triggering the error.

 Thanks Modzzz.  I will set you up tomorrow evening. It's been a long day of work and ready for bed.  I always appreciate your help. As always I will sift through your mods to see if I need anything to show my thanks for your support.