I was also having this error. I disabled the GTS plugin and all seemed to be well. However, I made the mistake of trying to reactivate it, and that caused my entire site to return 500 internal server errors, including my admin pages.
Thankfully after about 10 minutes I was able to get my wordpress admin panel to work just long enough to deactivate the plugin again and that seems to have removed the errors.
I would like to use this plugin in the future, but the errors are currently unacceptable.
