Correlation Issue - Instance Omitted

I've been trying to record a script that contains a dynamic value similar to session ID. During replay I see that the action isn't actually performed (I can see changes in the DB if it is) although LR reports no errors. From the result log, I found this :

-------------------------------------- 

Service: Reg Save Param Ex

TargetParam = XVAR

Left Boundary = LB=objHTTP.setRequestHeader("X-XVAR", '

Right Boundary = RB=')

Instance = Argument omitted

Result: Done

Time: 5/31/2013 - 12:58:24

--------------------------------------

Does the last line "Instance = Argument omitted" mean that the value for X-XVAR wasn't matched in the response? If not, then what does it mean? Any tips (or links) on how I can resolve a problem like this would also help.

Thanks,

Kumar