This has happened, so far, with a warlock and a mage now.
There have been two others that have had the issue as well.
Shortly after training my first batch of spells, I found that everything began to resist everything I cast. It did not matter whether the mob was gray, green, yellow or orange, everything was resisted.
I've tried creating a different character (thus the mage), clearing the cache, resetting the level and resetting all of the spells in hopes of correcting it.
After toying around with it, I found out by removing the Rockfury Bracers that I was wearing, I was able to cast again.
Edit: Then again, that didn't work RIGHT after. Upon taking off Pam's Prom Dress and the Rockfury Bracers, however, I had no issue.