Hi,
I'm using NI-IMAQ 2.6.1, Vision 6.1 and a PCI-1407.
I ran the following example installed from the driver:
C:\Program Files\National Instruments\NI-IMAQ\Sample\VB\Grab
and everything worked fine, so I was able to draw lines during the acquisition.
Try with this example to debug your issue.
Regards
AlbertoA