Occasionally subversion can get itself confused about what is and what is not in a working copy. This usually occurs if you have replaced the contents of a directory such as when you upgrade a component in Joomla!
You receive a message such containing this:
“working copy admin area is missing”
How to resolve this:
Step 1 — Rename the directory that is causing the error from a shell prompt and prefix it with __
mv com_docman __com_docman
Step 2 — Using your subversion client refresh your working copy, then “update” the directory that is causing the problem e.g. update com_docman.
Step 3 — Now you can commit the __com_docman directory.
After you have done this follow these steps, using your subversion client:
Step 4 — delete the com_docman directory from your working copy
Step 5 — rename __com_docman back to com_docman
Now “commit all” and both your working copy and repository will be in sync.
from http://www.recital.com/index.php?option=com_content&view=article&id=80:howto-fix-subversion-error-qworking-copy-admin-area-is-missingq&catid=67:developers&Itemid=101