UPDATE: Will Lennon has a new blog post with nicer instructions for investigating permissions in Web Access.
If you see one of the following errors when branching  or renaming a path in TFS:
TF14098: Access Denied: User DOMAIN\Bob needs Read permission(s) for $/p0/folder/*.
Or the following error when checking in:
TF14098: Access Denied: User DOMAIN\Bob needs Checkin permission(s) for $/p0/folder/*.
You can follow these steps to figure out which permission entries are blocking your operation. The instructions are for when you do not have Read permissions, but apply to Checkin permissions as well (just replace Read with Checkin)
These are the scenarios that can result in DOMAIN\Bob not having Read permission on $/p0/folder/a.txt
The Read permission is explicitly denied for $/p0/folder/a.txt for DOMAIN\Bob, or a group that he belongs to.
Note that group membership includes both direct and indirect membership (e.g. Bob belongs to subgroup which belongs to supergroup).
The Read permission is unset for a.txt and all parent folders that it's inheriting permissions from, for Bob or any groups he belongs to. Unset permissions default to implicitly denied.
Note that you can hit this case when permission inheritance is turned off for a.txt or one of it's parents.
The Read permission is explicitly denied on a parent of $/p0/folder/a.txt for DOMAIN\bob or a group that he belongs to. If this permission is not overridden at a lower level, $/p0/folder/a.txt will have inherit the deny entry.
If there are multiple applicable entries, denies will override allows. If Contributors are denied Read access, and Bob belongs to Contributors, giving Bob Read access will not actually give him Read access
The way to fix this is to either scope the deny down to a smaller group that Bob does not belong to, or turn off inheritance and leave permissions unset instead of using deny entries at all.
To diagnose what entry is causing issues :
- The following steps are only guaranteed to work if you authenticate as a member of the Team Foundation Administrators group (for the entire instance) or the Team Project Collection Administrators group. Being an ordinary user or a member of the Team Project Administrators group is insufficient. That is because if you do not have Read permissions, TFS will not tell you don’t have Read permissions. The exception is that the special Administrators groups are always allowed to see all paths and permissions. This is to keep Administrators from accidentally locking themselves out. Administrators will still get Access Denied errors, but they can at least see and fix the offending permissions entries.
- In a Visual Studio Command Prompt, run tfssecurity /imx DOMAIN\Bob /server:http://SERVER:8080/tfs to get the list of groups Bob belongs to, directly, or indirectly.
- In the same prompt, run tf permission $/p0/folder /recursive > out.txt, and open out.txt in a text editor that supports regex search (like Visual Studio):
- Note the use of the /recursive flag
- We are redirecting output to a text file because there may be ton of entries
- Search for any paths that include the following entries:
- “Inherit: No” where there is no explicit Allow: Read entry for the user or one of the groups he belongs to directly/indirectly
- “Deny.*Read” (use a regex search) for Bob or any groups that tfssecurity showed.
 We block server side branching (which checks in immediately without pending changes in your workspace) if you don't have recursive Read permissions on the source. Operations that result in server-side branches include:
- tf branch /checkin
- the VersionControlServer.CreateBranch() client object model call
- Branching from a Branch Object in Source Control Explorer
We do this because:
- If the user doesn't have Read permission on an item in the source, he shouldn't be allowed to branch that item
- If TFS offered to skip those items, it could only tell the user that one or more items will be skipped, not which items will be skipped. The user doesn't have Read permissions, so disclosing the affected paths could leak sensitive information.
- If we allow the user to skip any items, there is no way for the user to figure out if anything important is missing from the new branch without talking to an Admin. In that case, the user might as well have the Admin perform the branch anyway.
If you pend a branch instead (a non-server side branch), then we silently skip files with no Read perms. I consider that a bug (and have filed it): it should show a warning that one or more items couldn't be branched. Otherwise there is no way to trust that the branch is complete. Even an admin may be affected by explicit denies or disabled inheritance.