The problem is not that the DAG file is larger than 2GB, because it's not.
The problem is that for some reason OpenCL reports CL_DEVICE_MAX_MEM_ALLOC_SIZE: 1399062528, which the DAG file is now larger than.
The bigger issue here, is why does OpenCL think it can only allocate that much out of 2GB?
Need help ASAP!
Also, there are other reports of this issue popping up on Reddit and around the 'net.