I realize this is a year later, but for those who are still having or will have this issue, this was the fix and it worked for me (MBP 2.8Ghz Core2Duo, 10.7.5 running Compressor 3.5.3).
"Go to System Preferences and select "Sharing" Down the left hand side of the pop up box is a list of things you can decide to share. If you click on File Sharing, to the right of the list FTP Access : On will appear and in there is your computer's IP address e.g 10.1.8.6. Make a note of this number.
Open Compressor and go to Compressor > Preferences. At the bottom is a box headed: Enter IP addresses or ranges for manually selected computers; click the + bottom at bottom left. Put in the name of your computer and the IP address you made a note of. Then say OK.
When you open Compressor again and put a job in and press the submit button, lo and behold, in the drop down box, the Cluster now says "This Computer" and the submit button is no longer greyed out - BINGO!!!"
Source:
http://forums.creativecow.net/thread/200/888072