If you get “A General system error occurred: Timed waiting for vpxa to start” error when you try to add a ESXi 5.0 host to vCenter Server 5.0, this could be due to the number of snaphots saved for some of the VMs sitting on that server exceeding the recommended number of snapshots allowed.

These steps fixed the issue I encountered:

1. Check if you have any snapshots from the snapshot managers. If you cant see any probably coz you have a replication or backup software that keeps making snapshots in the background. So you can connect to the host using SSH and run this command to see what VMs are affected.
   find /vmfs/volumes/*/* -iname *delta*
   
2. Then connect to the host directly using vShpere Client software, and go to Snapshot manager and consolidate disks for the affected VMs.
3. Once done, try adding the host again to see if it works.