We had an issue with a single site in our Windows SharePoint Services (WSS) environment. The environment is set as a single site collection.
In a simple sense, the diagram above gives an idea of the basic layout. One main site which have very little if anything other than a way to get back and forth between the two sites. One site is limited to IT staff and the other is open to the IT staff and the department it supports.
The site Department 2 stopped being accessible over lunch one day. When trying to reach the site one would get "Cannot Complete This Action".
As long as one knew the address to sites under it they could get to them fine. Those with permissions could still upload documents to libraries, etc, but one could not create new lists, document libraries, etc. in that site or below.
If you put in the address of a known list or library in the Dept 2 site, one would still get the "Cannot Complete This Action" message.
Another symptom was that some links to site default pages were not working correctly. If a link went to a site without the default.aspx added (such as via the breadcrumbs), it may not find the default page. It seemed to consistently fail on the same place each time, but every site would not fail to load without the default.aspx.
Items within Department 2 would still display in search results and one could save the documents from the search and they would open fine locally.
We are in a mixed IIS and SharePoint environment. Our main Intranet site is still hosted on IIS and links to SharePoint for different items. As there were some documents that needed to be accessed within Department 2, and creating from the root worked fine, a Department 3 was created, and Department 2 documents were loaded into Department 3, links on the Intranet were updated and tabs that normally go to subsites of Department 2 were placed on the Department 3 site, but linked to the subsites under Department 3. We did not do this until we ended up being locked out of Dept 2 longer than we had hoped. All in all it took 2 1/2 days from start to finish to get things how they were.
A call was put in per a support contract to see if the issue could be resolved.
Once getting the callback after putting in the initial problem, it was cleared up rather quickly by a hotfix that one would not have guessed would eliminate the issue, but since it did, who can complain.
That doesn't mean it will fix your problem as we found a lot of individuals with the issue vai online search and some recommendations out there that a few seemed to work for a few, but not others, so as they say, your results may vary.