The file system actions don't seem to be documented in the help so I don't know if they still apply but check if one of the roles assigned to your user has the XMII_FileSystem_RW ume action assigned to it.
The file system actions don't seem to be documented in the help so I don't know if they still apply but check if one of the roles assigned to your user has the XMII_FileSystem_RW ume action assigned to it.