Yup, I have the same error. We are playing the map on my server, and it worked for people who already had it, but once new players wanted to connect, they got the above mentioned error.
The only way to resolve it was deleting the map from the server and manually from everyone's folders so it would download it new. But that (current) version is an older one.

Hey, I don't know what would cause this.
If it's a dedicated server make sure you launch the map via "host_workshop_map 1485909129" instead of "map de_drachenschanze_csgo". That will always pull the latest version off the steam workshop.

Also, make sure you haven't subscribed to the beta version of the map (steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2303508894) as that has the same BSP name and might mess things up.

Hey, it seemed to work again. Not sure what has caused it, I deleted the map from the server and it would download the correct (300mb) version again, before it only had the old (130mb) one.
Thanks!