Okay, so I'm running Win 10 1703 x64, and mameui64.
I've tried both the official build and a fresh compile of tag189.
Two things are happening:
1. Cannot change background without crash. Managed to change it by cut/paste from the old .ini. Once that is done, the background image changes fine.
2. Software lists do not appear in the software picker. The pane is blank. I use a "software" folder to keep the software roms (rather than the "roms" folder, which only keeps the system roms), and it is properly pathed in mameui64's directory settings. The ROMs path points both to .\roms and .\software.
I managed to fix the icon problem by auditing all the ROMS. I'm sorry I didn't read the changelog first regarding the ini. Deleting the ini's was the first thing I tried.
3. There is no directory setting for the ini directory in the drop down list. This may be in the changelog.