RAM Compatibility

A few days ago I sold 4x 1GB sticks of DDR2 RAM on eBay, but the buyer says that the sticks of RAM will not run on dual-channel on their motherboard.
A picture of the four sticks of RAM is here:



This RAM ran fine on my old motherboard on dual-channel, can the RAM safely be used on the buyer's motherboard in the same configuration?
Apparently the buyer's motherboard is 11 years old and their system runs Linux, the buyer also complains about the speed differences in the RAM; would there be any noticeable difference in the RAM speed?

Thanks