That solved that problem, however I think that I have found a bug in the driver. It had been causing me grief for the last few days.
In the past on the 3000 series scopes, I never used the "getTimebase" function, because I calculated all other information on my own. Which this is fine, because that is only supposed to be the way to determine what timebase to use. You are supposed to specify the timebase in the "runblock" method. Given that you did everything correctly, it should work as normal.
In the 4000 series, you MUST use the "getTimebase" method, because otherwise (maybe always) it completely ignores the argument "timebase" in the runblock command. The second bug, is if you use the getTimebase function, make sure that you set the oversample to 1. If you set it to 0, the function will return a 0 or PICO_OK, but the data that is returned is non-sense.