Just to ass to the ongoing fun of this...
This issue reared it's head again. This time I noticed it in the patcher before getting ingame, though I logged in and confirmed the issue.
The Macroquest folder had somehow come up as "read only" with needing admin permission to alter. Trying to alter this as a user appeared to work... but rechecking the folder it came up as read only again /boggle
Making a new folder did (again) "solve" this issue for me... but since its repeating, i started pounding a hammer on the PC until it coughed up some some potential issues.
One potential was apparently windows security... except I use Avast.
Logged is as administrator, changed the folder properties to remove read only, made exception for the folder Macroquest is in, logged back as a user, macroquest was able to update and operate (and RGmercs able to run)
Not sure why avast would pick today to have issues with something as opposed to the last several months... if this is the issue. Had not previously made exceptions since it has not previously been an issue.
Posting in case this helps someone else. Will repost it if happened again.