"Domain already in use" error when I try to park domain

[StupidCatOfDoom]

The first time I tried to park the domain scodtv.be in cPanel, it didn't work because i'd forgot to change the domain's nameservers to the x10 nameservers. When I went back to change it, it said it was already in use by another user. I'm confused; what do I have to do, wait 15 minutes for eurodns.com to switch my domain over to the x10 nameservers? Or is it really owned by another user?