My advice - call your reseller, or Sage tech support.  Interrupted updates can be very tricky to find & fix all the problems.

You need to contact either your reseller or Sage Tech support. This is a serious issue that must be understood to be correctly fixed. From what you have posted I can say that someone was updating, it crashed for whatever reason. The system wants to restart the update but the AR Invoice Data Entry file is locked somehow. It needs to be unlocked so the update process can continue. Also since you indicated AR5ARC  this indicates this is 3.XX or maybe v4.0 of MAS meaning that all support has stopped with Sage.  Personally I would track down Alnoor Cassim on here. He would be able to help/fix.

Note that if you try to fix without fully understand what is happening you could easily get any number of files out of sync or with bad data.

I solved my problem by just loading the last complete backup to another machine and was able to access it. I was hoping there'd be simple answer to the problem. Live and learn. Thanks for the help.