Subclipse complains “Path is not a working copy” after moving workspace

You need to delete the .syncinfo files. This is easily done (in most cases) by closing and opening Eclipse, however you can also do so manually as in the following:

To delete the cache, close Eclipse. The cache is stored in:

[workspace]/.metadat​a/.plugins/org.eclip​se.core.resources/.p​rojects/PROJECTNAME/​.syncinfo

So you can just find and delete all files named .syncinfo in

[workspace]/.metadat​a/.plugins/org.eclip​se.core.resources/.p​rojects

Quoted from this article: http://subclipse.tigris.org/ds/viewMessage.do?dsForumId=1047&dsMessageId=868799