The Web site address “/sites/T3W-PM/010101140819” is already in use

I’ve created a workflow to automate the subsite creation process as much as possible. This has worked perfectly for several day, however. I came in this morning and found that every requested site is returning the following error:

The Web site address "/sites/T3W-PM/010101140819" is already in use. 

It is not possible for the addresses to be in use as the address incorporates a unique project number which is generated at site creation and cannot be repeated.

I have checked the subsites list and the error-ed site do NOT appear to be there. I have also checked the workflow and there is no recursion, that I can identify, which might cause the HTTP call to fire twice.