VSTA ProjectAddin not being executed?

VSTA ProjectAddin not being executed?

I'm trying to implement OnlineContainer functionality to perform certain actions if a variable received from the PLC is changed. I've copied and implemented the code from the tutorial in this forum. However, the code isn't being executed. I've tried adding messageboxes and putting breaks in the code, but even InternalStartup isn't being executed.
Any ideas what could be wrong?

This is a migrated post! Originally posted on 09.01.2015 by user pbo. Please be aware that information can be outdated.