Mokey-Remove/Matte Extract memory allocation

Hi Guys

I have a 1920 x1080 clip 138frms in length. 2 layers. 1st - loose garbage track matte for forground actor. 2nd - large track matte for Background. Everything tracks fine, but when I go to remove the actor and perform the Remove before the Matte extract I get the error:

‘Failed to allocate memory buffer. Please free up system memory by closing other applications.’

I have no other apps open. I’m running a dual quad core with 4GB Ram and 50Gb free space on local drive. Had the same reaction running on other machines and or using space locally or on the server.

Has anyone got a work arround or seen this before.