It was a generic windows 10 error. Like file not found, or source not found, even though the file IDM.exe was there. When I looked on the microsoft site one of the suggestions was if the program didn't have permission to interact with the file.
There is no Avast warning that pops up. It just blocks it and windows pops up the error message. Only way to get it to update is to drop the shields until it updates the IDM.exe file.
I noticed this thread is talking about a similar issue:
https://forum.avast.com/index.php?topic=180336.0I just tried updating to 6.25 Build 8 Final and avast! blocks IDMan.exe and halts the update process. It's a legitimate copy of the program trying to update itself. Had to temporarily disable avast! in order to update IDM.
His version was version was 6.25 Build 8 Final. Mine is very 6.25 Build 12 Final.
Edit: It's like Avast isn't taking notice of the exclusion list. I had a similar issue a year ago on the WinXP IDM update. I ended up adding IDM.exe to the Avast exclusion list and it worked. I've added IDM.exe to the version on the Win10 computer. But it still interferes.