Hi there,
Been using auto-numbering for many years (thank you for mp3tag, by the way, it's really useful). This week, though, the auto-numbering wizard has stopped functioning. The Wizard pops up but clicking OK doesn't produce any results. 
I've uninstalled, reinstalled with no change. OS is Windows 10 Pro
Could you tell us what you expected to happen?
I just tried the very same settings on a number of files and the track number changed as expected, i.e. first file got 1 and the 13th 13.
Thanks. I expected it to do the same with one slight difference - I generally use the function to put a leading zero on tracks 1 to 9.
Up until a few days ago, clicking OK caused the wizard to close and the tracks to be numbered sequentially in the order they appear in the main window.
Uninstalled using Revo Uninstaller with an Advanced Scan.
Upon subsequent re-installation, the wizard now works.
There are some audio file formats that do not accept leading zero. Like m4a for example.
Indeed, though this was every file of any type that the wizard didn't work for. No matter, all working now after a thorough deinstall & reinstall.
I didn't know this existed because I use an "Action". If it breaks again, create a new "Replace with Regular Expression" action.
Field: TRACK
Regular expression: ^(\d)$
Replaces matches with 0$1
Just select all your tracks, execute that action and all of the tracks without leading zeroes now will. 
Thank you! I didn't know actions existed.
Every day's a school day.
If you do not feel at home with regular expression, then an action of the type "Format value" for TRACK and
Format string: $num(%track%,2)
for 2 digits
or even
Format string: $num(%track%,3)
for 3 digits
would also add padding with zeros where required.
There are many ways to skin a cat.
