The webservice is responding that the agent from a failover pair is offline while it's not.
If I send a command over vpn to the agent it responds it's offline.
When I perform the command on the server itself it's giving me a guid.
I think that somewhere DataMiner thinks it's offline while it's not.
Is there somewhere a file I can check?
When a DMA of a failover pair goes offline, then IIS rewrite rules are activated that respond with an error message to indicate that the DMA is not online. When the DMA goes back online, these rewrite rules should be deactivated again. You can find these in the web.config file in the Webpages folder, and also in IIS Manager under URL Rewrite. There is an exception on these rewrite rules, local requests from the server itself are not altered, so that's why it works for you on the server.
We've seen this issue before with failover pairs using hostnames. Is this also the case here?
Removing the rewrite rules fixed the webservice