[Solved]-Strange Play Framework 2.2 exceptions after trying to add MySQL / slick-scala

Well, I finally figured it out. I feel like a bit of a dolt, but I'll post it here since it may be useful to someone else:

During earlier work on my project, I was experimenting with other potential libraries for various things: Mongo, BSON converters, etc. Of course, while experimenting, I was adding them to my IDE's project library dependencies (I'm using IntelliJ IDEA 12). Naturally, IntelliJ was downloading the JARs and placing them into my project's lib directory. However, after settling on the libraries that I wanted to use and removing the unnecessary ones from my project dependencies, IntelliJ did NOT delete/clean out the unused JARs from my project's lib directory. This resulted in a whole bunch of unnecessary JARs being in there, some of which presumably conflicted with the SBT libs.

In short: I cleaned out my Play project's lib directory, double-checked my project's library dependencies in the IDE, and re-imported only the JARs that I really needed.