If you receive the error below while adding a host to your vCenter server:
A general system error occurred:Timed waiting for vpxa to start
All you need to do is update your vCenter instance. For example, if you are running vCenter Server 5.0, you cannot add an ESXi v5.1 host to your vCenter instance.
The solution in the following KB
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http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2009217
@Mohamed, thank you for the reply! It looks like this appears to be a generic error for multiple issues. Unfortunately, I didn't grab the log file when I was getting this error when adding my machine to vCenter, so it is great you provided feedback when receiving the error from a different action.