Hi,
I haven't worked with this particular instrument, but I looked into the instrument driver and I can't figure out exactly what you are asking.
I checked the "HP 3458A Read Digital Sample Memory.vi". It does send as you mention the "END ON;RMEM 1,100;" command. The VI does not check for error conditions in the instrument. You can use the utility function "HP 3458A Utility Error Query.vi" to ask the instrument if any errors occurred.
Is the instrument giving an error?. What error is it?
DiegoF
National Instruments.