Ram tests OK separately but gives ERROR together. Help!

Hi,
I hope somebody knows what's going on here. I have purchased two 4GB ram modules to upgrade my MBP from 2GB.
I have installed the two 4gig ram and everything seems fine but read on the net that it's the best to test your new rams so I've ran Rember which gave me errors as follows:
-------------------------------------------------------------------------------- --------------------------------------------------------
Memtest version 4.22 (64-bit)
Copyright (C) 2004 Charles Cazabon
Copyright (C) 2004-2008 Tony Scaminaci (Macintosh port)
Licensed under the GNU General Public License version 2 only


Mac OS X 10.7.2 (11C74) running in multiuser mode
Memory Page Size: 4096
System has 2 Intel core(s) with SSE
Requested memory: 6783MB (7112953856 bytes)
Available memory: 6783MB (7112953856 bytes)
Allocated memory: 6783MB (7112953856 bytes) at local address 0x0000000101000000
Attempting memory lock... locked successfully
Partitioning memory into 2 comparison buffers...
Buffer A: 3391MB (3556476928 bytes) starts at local address 0x0000000101000000
Buffer B: 3391MB (3556476928 bytes) starts at local address 0x00000001d4fb8800


Running 2 test sequences... (CTRL-C to quit)


Test sequence 1 of 2:


Running tests on full 6783MB region...
Stuck Address : setting 1 of 16 ok
Linear PRN : setting 1 of 16 ok
Running comparison tests using 3391MB buffers...
Random Value : \ ok
Compare XOR : ok
Compare SUB : ok
Compare MUL : ok
Compare DIV : ok
Compare OR : ok
Compare AND : ok
Sequential Increment: ok
Solid Bits : setting 1 of 64 ok
Block Sequential : setting 1 of 256 ok
Checkerboard : setting 1 of 64


FAILURE! Data mismatch at local BUFA address 0x0000000127c02760, BUFB address 0x00000001fbbbaf60
BUFA Data: 0x5555555555555555, BUFB Data: 0x5555555555557555


Bit Spread : setting 1 of 128
-------------------------------------------------------------------------------- --------------------------------------------------------------------------------
So I have run Memtest86 (booting from a CD) and it also shows several errors (which I have no logs from) so I have removed one of the ram and re-run both tests. It passed both tests with flying colors so I have swapped the rams and ran both tests on the other one too. Same thing: no errors deteced.
Now I'm kinda puzzled. Should I return the rams and ask for new ones or what?

 

It says 8GB installed; everything is okay there.

 

Yupp. That's what i'm going to do. Thanks!