As addition to the hints from @ttrafelet i would said that the file not found is something that happens after the upgrade to 2.0 if you had before some checks installed inside local/share/check_mk/checks. But this message als stays after you removed the old plugins. The cause for this is that CMK caches the precompiled checks inside the following folders.
~/tmp/check_mk/check_includes/local
and
~/var/check_mk/precompiled_checks/local
If you cleanup booth folders and get again the error message then there must be some old plugins inside local/share/check_mk/checks who try to use these files.
Here inside this Werk you find the description what needs to be done with old plugins and includes.
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