It appears the latest 1.2.9 update to DCS World has defaulted the tanker communications to 251 AM.
Unfortunately our Air to Air Refueling missions had the tankers coded to use 150 AM so using these instructions will no longer work.
We will be updating the mission documentation to use the 251 AM setting going forward.
For now if you are using DCS World 1.2.9 and any AAR mission instructing to contact the tanker on 150 AM, use 251 AM on the UHF radio instead.
By using the default 251 UHF AM setting going forward we hope to avoid issues like this with future DCS World updates.