With ETH reaching epoch #379 Claymore mining client stopped working properly on all rigs - doesn't matter how many GB the card has.
The error on Claymore will show DAG generation error or different error messages such as clcreatebuffer(-61).
To solve this issue, you will need to use a different mining client. A list of supported mining clients for ETH can be found on ETH mining calculator page on the left sidebar with Phoenix, TeamRedMiner, lolMiner, NBMiner, Nanominer and T-Rex being recommended for first try: