With the latest 1.7.2 FML, we saw errors like this on two different systems:
java.lang.RuntimeException: Unknown character '' in 'C:/Users/name/AppData/Roaming/.minecraft/config/CustomSpawner/Global.cfg:1'
Both of these systems have the Mo'Creatures mod along with Custom Mob Spawner. Both of these systems were playing against a compatible Cauldron server with no issue, but within a couple days we got the above error.
On one system, as above, the CMS Global.cfg was present but was empty.
On the other system, it was the MoCreatures.cfg that was present but empty.
Or rather, editing with WordPad (only tool present on those player systems) it looks like all of the text in the files had been replaced with spaces.
I did not check the files with a binary editor, the text might have been converted to UTF16 or otherwise corrupted so that it just looked like they were cleared.
The issue was resolved by simply restoring the data to the files from another system and restarting the game. (Could have just replaced the files, didn't realize that on first look.)
A Google search for "unknown character customspawner global.cfg" returns a number of hits indicating this has happened elsewhere and that it's probably related to Forge.
I understand Forge is now supporting MC 1.7.10 and we'll upgrade soon (now that Cauldron supports this release as well). I just wanted to post this in case the problem occurs elsewhere, in case some other admin needs a resolution, in case the problem somehow carries into the latest releases, and/or in case a developer wants to see if there's any way that Forge would update a mod .cfg file (or in some way cause a mod to do this to itself).
Thanks.