I encountered a problem earlier this week provisioning a new ConfigMgr 2012 environment with a State Migration Point (SMP).  I am used to just installing the SMP role and pointing it at a drive letter to use and letting it create the folder structure it needs.  However, I think there may be an issue with ConfigMgr 2012 with this method as it seems to want to modify the permissions of the folder that you specify, and if this happens to be the drive root then we see some problems.

When attempting to install the SMP role and specifying the drive root as a target, the SMPMGR.LOG records the following errors continually;

What seems to happen is that the SMP role setup routine modifies the permissions of the target folder and now has insufficient permissions to create the necessary MigrationStatus folder within the SMPSTOREF_12345678$ folder.  This issue does not occur if you use the drive root which ConfigMgr is installed on as a target, weird.

So in summary, you must create a sub-folder (maybe called SMP or SMSSMP) on the drive you intend to use for your SMP role and use that path as the target, never the drive root itself.