Very perplexing forum issue [INVALID SPECIFIED] Some accounts unable to see forum
 

Literally pulling my hair out over this issue. Some users reported getting an error message, "Invalid specified. If you followed a valid link notify the administrator" message, when clicking on one of my forums. The other forums can be viewed with no problem.

When I log on with my admin account, I can see this forum fine, yet, when I log on with my "regular member" account, I too get this error message.

To make matters more confusing, some members can see the forum fine, others get the error link. It should be noted that those who can see it and those who can't seem to be random. All are regular members with the same level of access.

I have not changed any permissions lately, and when I check permissions in the Admin panel, I see the appropriate level of access and peple should be able to see the forum in questiion,

A test forum I created using a clone of this problem forum did not have the same error issues.

Please help.