In general, other Wait activity in the GUI - for this we need to click on the wait event to know exactly which wait event is causing this. This is usually a normal behavior happening on some Oracle instances. The other wait category represents activity which where not categorized as part of any other categories.
In the case where we see Error Event when clicking on Wait Events chart, then this is a known a collector issue that was fixed in the 6.3 version of the collector. What happens is that Linux has a collision table with processes status codes (as S for sleep etc.), that PA reads from and translates.
In pre-6.3 SC versions, some of those values were not trapped and PA reported as errors. Please upgrade your agent to 6.3; that should solve this issue.
To download the agent for your platform:
1) Go to http://support.quest.com/
2) Click on "Downloads & Updates"
3) Type in "Performance Analysis Oracle" for the product and click "Go."
4) Click on "6.3" for the product version.
5) Click on your platform under the "Platforms" section.
6) The download link will appear for the local server installer for your platform.