ps6000aSetChannelOn gives inconsistent result

[rameshrathinam]

I am using ps6000a.dll to interact with Pico 6424E.
I am success in ps6000aOpenUnit and ps6000aGetUnitInfo
Driver Ver: ps6000a Win?
USB Ver: 3.0?
Hardware Ver: 1.2?
Variant: 6424E?
Batch / Serial: JY984/0040?
Cal Date: 24Oct22?
Kernel Driver Ver: 1.0?
Digital H/W Ver: 1?
Analogue H/W Ver: 2?
Firmware Ver: 1.7.16.0?
I am wondering what is the ‘?’ at the end of each string.

My attempt to ps6000aSetChannelOn gives inconsistent result, I have to set Channel A and Channel C. My first call fails most of the time while my second call fails always. When it fails, the return code is &H10E (PICO_INVALID_BANDWIDTH). I tried all available options PICO_BW_FULL, PICO_BW_20MHZ and PICO_BW_200MHZ, inconsistent behaviour is the result. What am I missing?

RetStatus = ps6000aSetChannelOn(deviceID, PicoChannel.PICO_CHANNEL_C, PicoCoupling.PICO_DC_1M, PicoVoltageRange.PICO_5V, CSng(0.0), PicoBandwidthLimiter.PICO_BW_FULL)
If RetStatus <> PICO_OK Then
MsgBox("Error setting channel A " & deviceID & “ , “ & status,)
Return False
End If
RetStatus = ps6000aSetChannelOn(deviceID, PicoChannel.PICO_CHANNEL_C, PicoCoupling.PICO_DC_1M, PicoVoltageRange.PICO_5V, CSng(0.0), PicoBandwidthLimiter.PICO_BW_FULL)
If RetStatus <> PICO_OK Then
MsgBox("Error setting channel C " & deviceID & “ , “ & status)
Return False
End If