Hi,
I know that is a very common issue, but me too had a problem with DAG file.

I am testing a AMD RX 570 Pulse (8 GB), with 8 GB of RAM, 16 GB file paging.
Using Claymore system says: "OpenCL error - cannot allocate big buffer for DAG. Check readme.txt for possible solutions", altough I put -eres 0 in line command.

Now I am testing mining with Phoenixminer and there is no problem with DAG file.
How is it possible?!

Thanks and excuse me for my bad english!