Propane tank won't fill

My van has been sitting with an empty propane tank for about two months on the driveway.

This morning I went to fill the tank and the tank would not fill. It was trying to fill but it was almost like a blockage.

After several tries we slowly got just over a gallon but the guy said he didn't want to do any more. He didn't charge me for the gallon.

Any ideas what may be wrong ?:confused::confused:

Thanks

Colin