I've included the 3 most common reasons we experience the Create New Local checkbox being disabled when a project file is highlighted.
1. Are all users mapped to the central file the same?
9 times out of 10 this is the culprit. Since Revit saves the location of the central file, it will detect if a user is accessing the file differently. This is an easy one to check if you have 2 users, for example, where 1 can synchronize with central and the other cannot.
If a user is not able to utilize Create New Local, have then instead attempt to open the central file after browsing to the location in Revit. They will most likely see a dialog similar to the image below during file open:
If they see this message it should indicate how Revit sees the file mapping variance.
You can easily reproduce this issue if you have 2 users accessing a project file. Say they are mapped to the server as follows:
UserA - Z:\Projects\ProjectX
UserB - \\ServerA\Residential\2010\Projects\ProjectX
User A has a mapped drive letter directly to the Projects folder, where UserB has the full UNC path. If UserA opened and saved the project as a central file, Create New Local would work fine for them. If UserB then attempts to create a new local file it will be grayed out as the location mapping varies.
Bottom line; all users need to be mapped to the server location where the central file is stored in exactly the same manner [UNC path, IP Address, etc]. Technical solution available here mentions this issue as well.
2. Worksharing is not enabled in the project file
Easy one to eliminate as the potential cause. It's a quick item to check if you open the project and see if Worksharing is enabled under Collaborate > Worksets.
3. Central File Corrupt \ Thumbnail Locking Issue
Not nearly as common, but if the user cannot create a local file have them attempt to open the central file.
If they cannot open the central file, have another user attempt to open the central file to rule out #1.
If no user can open the central file, is it giving an error message? Or does Revit simply appear to be frozen?
If you receive a corrupt file, invalid file handle, or past its end message the central file may need to be recovered from backups. If Revit simply hangs, you can rule out a potential thumbnail locking issue from our previous post here.
Please feel free to add any additional scenarios you may have encountered!