keithley 2400 ramping buffer read

[mischi_miyagi]

Hi,
I'm struggling at the moment with the attached VI using LabView 8.2, a Keithley 2400 Sourcemeter with a Keithley KUSB-488 USB-GPIB adapter. I want to run different ramping voltages (at the moment only linear ramping is programmed) measuring current. When I'm starting the program I get two error messages from the 2400 (-201, -420), then the voltage is properly ramped but the buffer is not read and I got a timeout error from "Wait for RQS". The funny thing is when I'm running an example program from Labview and then run my VI afterwards the currents can be read. When I now add a while loop between the VISA Event Icons I can read the currents one time but then I'm getting the timeout error again...
I want to stay with the VISA programming (and not with the 24xx-driver pallette) because this is only a small part of a bigger, more flexible program including more instruments.
I think I've done somethin wrong with either the instrument commands or the sequence for the buffer read...
I would be very thankful if someone can give some hints for my problem...thx.

Regards,
Mike

[mischi_miyagi]

Me again,
I've done some smaller, simpler VI with a while loop (please find attached). The also attached sceen is from NI-Spy doing the while loop three times...also the errors on the 2400 (-201, -420) are still there but when I'm running the program the second time (without restarting the 2400) they do not show up.
So, if someone has an idea...

Regards,
Mike

[mischi_miyagi]

OK, have fixed the loop problem...very stupid mistake, forgot to enable buffer tracing...grrrr.
But still have those irritating errors from the Keithley 2400 but for that I will contact Keithley...

Regards,
Mike