Why is @Grapes causing exceptions in my Groovy plugin?

It seems that the issue you are facing is related to an open ticket: RTFACT-6759.

The embedded Groovy may have problems when @Grapes finds dependencies that are already included in Artifactory itself.

 

In order to solve this issue you can remove the use of @Grapes and instead place your libraries:

dforg.codehaus.groovy.modules.http-builder

oauth.signpost, module

oauth.signpost, module

 

under $ARTIFACTORY_HOME/etc/plugin/libs

 

You will need to upgrade your Artifactory to our latest version because the ability to load libraries from the libs directory was added recently. (RTFACT-6562).