Custom check not getting executed - permanent staying as pending

Hello Everyone,

has someone else any idea why I am not getting the plugin output to nagios?
If needed I can of cause provide logfiles, but i am currently at a loss where to search for error messages or any lead to a solution.

On a side note:
If I change the the group in the check declaration to group : "ps" , which is the same group the default checks ps and ps.perf use, I get the following error:

Checkgroup ps has checks with and without item! At least one of the checks in this group needs to be changed (With item: ps, ps.perf, Without item: ps.posa)

Has anyone an idea of what this ‘item’ is and what check_mk is expecting my plugin to return?
I can remember reading of it somewhere, but the article was incomplet and i currently can’t find the article anymore.