ofxTweener on Windows - '^' requires '/clr' or '/ZW' command line option

Hi,
I’m running into troubles with ofxTweener, of8.3 on Windows 8.1.
Using VS2012 I’m getting the following error message:

error C3193: ‘^’ : requires ‘/clr’ or ‘/ZW’ command line option

I guess I could avoid this problem by using an older version of ofxTweener which doesn’t use ^callback. However I’d like to understand what’s going on. Any ideas?