Hello Trevor, don't panic!
The error messages you mentioned were no real error messages, actually. Let me explain. The text output of LZX unpacker seems to be confused when unpacking files with zero size. In this case the LZX displays inappropriate error message: Error writing to disk. Disk full?
. However the files themselves are unpacked correctly. No need to worry.
When I was preparing the update I had two possibilities. To hide the text output of the unpacker completely (like I did with all the previous AmiKit updates) or to show the output. I decided to display the output because this particular update archive is very large and its unpacking takes much time - and if there's no output to the screen it could look like the AmiKit had frozen and the update doesn't work, you know.
Anyway, the fix of the unfinished update process is very simple. It is enough to apply the update again but before you do so, make sure the AmiKit thinks it's still 1.3.7 version.
Edit the following file:AmiKit:Prefs/Env-Archive/AmiKitVersion
and change its content from 140
. Save the changes and quit the emulation. Now apply the 137to140 update again and everything should be fine.