Yes it is strange for me too. I have more than 1 person that having the same permission/tablink/group but doesn't get the error, while 1 user get the error and sometimes the error switched to other user.
Its happening on button click. When the user wants to Log a Call.
When the button is clicked, usually it load the contact's detail, company details, previous activity details, and contact form in pop up screen. But in the case of error, not even the pop up screen shown. If the error are located at the screen load, then the pop up screen should show first then error.
Additionally we haven't heard any error for this week, but nothing that I did previously. So its a bit odd. Please let me know if you would like to have access into the account.