I read on TechNet that you can't attach the same content base two times to the same farm http://technet.microsoft.com/en-us/library/cc263299.aspx#restore
We are going to try a migration soon, and I think that it has beed tries before (just got the task). Is it ok to detach the old version of the content base, then upgrade the new version and use that on the same site collection? The reason is that whey have continued using the old 2007 and would like to move the new content to the 2010 farm. Or is there a better approch?