Lately I have been having more and more issues with the content assist in Eclipse. In some of my projects, I get no proposals from the content assist, and in other projects
I had this problem too, with Pb(324) message. It turned out, that reading the message with understanding was enough to fix it. However what I did first was going to stackoverflow. No good :)
In my groovy project the dependent libraries were not automatically visible by autocompletion. Not sure why, I'm new to this stuff. So I was adding them manually. But I did not add manually the indirect dependencies. The error message specifies the class causing the problem. I added a reference to the jar containing the problematic class and bingo - no more code assist errors.
To be specific: Project, Properties, Java Build Path, Libraries, Add External JARs. Then I pointed to the directory, where gradle downloaded the lib.