"Can't load factory class for node" under Mac OSX

I'm using Knime v2.7.4 under Mac OS X 10.8.4 after installing my node via updatesite I get following error:

2013-05-28 12:15:46,068 ERROR Worker-1 RepositoryManager : Node org.BioRS.queryreader.BioRSQueryReaderNodeFactory' from plugin 'org.BioRS.queryreader' could not be created: Can't load factory class for node: org.BioRS.queryreader.BioRSQueryReaderNodeFactory The corresponding plugin bundle could not be activated!

Installing and running the node under linux and windows functions properly. The knime.log and .log files contain no further errors. I'm using external libraries but included them using the method described on your website.

I'm pretty clueless regarding the error.

You have compiled your code for Java 7 but KNIME runs with Java 6 on MacOSX.