System lockup problem when adding more memory - FC5

[Cokey]

I have an older dual processor server that has been happily running FC5 
since it was released.  It currently has 4G of memory and has the 
capacity for 8G using 1G sticks.   Recently I was given 2 1G sticks and 
tried to upgrade the system.  The system recognizes the memory and 
boots, but then locks up with:

exec of initj(/sbin/init) failed: Exec format error. 

Removing the memory clears the problem.  I have also tried some 512 
sticks and they also cause the same problem.  Essentially anything over 
4G regardless of the how that's arrived at will cause the lockup.

Looking for any hints/ideas.

Tnx

Cokey
 

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