It's hard to pinpoint the error, especially if I can't reproduce it and apparently, all other users don't have the same problem.
What you can do (provided you're an advanced user/admin) is to go into your phpmyadmin into your vbulletin database, open the table #_datastore (where # is your vb table prefix), search for the entry with title "steam_softlinks" (should be the last entry) and check if it's not empty and if your steam-id is stored there.
For your steam-id to be resolved to the numeric expression, you can use this tool:
http://steamidconverter.com/
It's the steamid64 number you're looking for.
If the id is NOT found, then there's something wrong with your steam-id and/or steam not returning your steamid for any reason.
However, I'll check this out as soon as I got more info on what's happening there on your machine.
That's all I can do from here right now.