Out Of Memory

Hey recently, cross fire would randomly force close then error comes up. Out of memory. All you can do is click ok.
My pc specs are:
Gpu: nvidia gt745m 2bg dedicated card + intel hd 4600 graphics
CPU: intel core i7 4700MQ @2.4 Ghz per core ( turbo boost to 3.40ghz) quad core hyper threaded (8 logical processors)
Ram: 8Gb ddr3 1600mhz ram. *4gb used before crossfire opens.*
HDD: 1000gb hybrid hdd. *880 gb left*

What could be causing this error?

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