I think I figured out what was going on. In addition to the typos on the signup variables, there were two items that were flip-flopped. Once I traded places with these two buggers... everything seemed to work.
You are looking for DATELINE_TO_USER and DATELINE_FROM_USER... they only appear once in the XML... just flip-flop them and you should be good. At least everything started working for me. Once the change was made, single-event signup started working and I was unable to sign up for events that had already passed.
If you already have 1.07 installed, but not working correctly, simply make the changes to the XML and re-import it (I did it with overwrite enabled). If you're not comfortable with editing the XML file... I've attached mine. Just be aware that this may not have solved ALL problems, but it did resolve mine as far as I can tell thus far.
I'm just stoked 'cause I get to start using this mod again!