Unfortunately due to hack usage in SA-MP, the d3d9.dll usage is prohibited by the San Andreas Multiplayer Modification client. The ENBSeries modification uses to my knowladge uses the d3d9.dll, so the client will automatically cause your game to cease working when attempting to play, in order to fix this issue please remove the d3d9.dll from your Grand Theft Auto San Andreas folder.
If you think this is unfair or unnessacary precautions taken against hacking, please do contact team@sa-mp.com.