Hopefully I can try to help on this one. You are allowed a one-time switch to per-seat, which you have done. You also made your changes to the Licensing Manager and agreed to the terms. So, it seems you have done everything right. However, as opposed to per server licensing, per seat works from the top down. You use License Manager to install licenses on a license server (housed on pdc). The step I couldn't tell if you took was to then go to the servers being accessed and makes sure they are too per-seat. Utilization data is replicated up to the license server where it is compared to registered licenses to monitor compliance. if this update isn't found to be in compliance, the license addition will not take. Configure each NT server on domain as follows:
Use license manager to add licenses to license server that replicates lic. info for domain or enterprise as appropriate (pdc).
Open Licensing utility in control panel.
If multiple products are listed in the product field, select windows NT Server
In choose licensing mode dialog box select per-seat. You must ensure number of computers on network does not exceed the total number of licenses you have added.
Configure replication: Most likely you will want to choose Domain Contoller. Then specify a frequency (try to set to replicate during non-peak hours).
The exit license utility.
Remember, since per-seat works from top down, you have to configure all servers being accessed by PDC and users for per-seat andthe above steps due to replication process. I hope this helps and I think this will. Let me know if something doesn't work in regards to this.