If an initial Subversion checkout is done as "Empty" or "Immediates" from an existing subversion (server) repository, Toad won't allow to drill down into the sub-folders when setting up Team Coding and selecting a server project.
This is because the Subversion client is trying to execute the command from the local matching subfolder which doesn't exist because of the initial checkout level.
WORKAROUND
none
STATUS
waiting to be fixed in a future release of Toad For Oracle.