At the moment i'm doing a lot of web farm installations at different customers. What i noticed is that in some cases suddenly functionality stopped working within Central Administration like changing authentication providers, creating web applications or site collections and more. The following is shown and just doesn't tell you much.
The path specified cannot be used at this time. (Exception from HRESULT: 0x80070094)
I tried to figure out whats causing this but got strangled in unreadable logfiles, eventviewers en blogs on the internet. Finally i figured out that their are 3 things you could do to resolve this. Just try them one by one and test every time in between if it resolved the problem.
1) Do an iisreset or a recycling of the application pool
2) Restart the SharePoint Timer Services
3) Restart the server
I know the last one is actually ridiculous but it helped. Good Luck!!