Had the same issue, PMS has been up and running for about 4 years and when I relocated the server it would not connect! After I read your post I checked regedit, lo and behold I had forgotten that I had mapped the meta data to a NAS that I had not re mapped on the new network location ( 1.5TB Metadata Folder 
) so after remapping the drive in explorer (I did not change my settings in the registry just pointed PMS in the right direction) It still did not see it so like everyone should know I turned it off and back on again, lol. Upon restart the service auto ran and updated library.
Thank You for your post and it is sill relevant 3 years later!!
