Splitting PFI lines between multiple tasks

I'm trying to write to two different PFI lines.  I'd rather have them in separate tasks because they'll need to have different length wavefroms, which would make updating them at the same time difficult.  I tried this:

http://pastebin.com/27g8pKhs

Basically I setup two identical tasks, one for line 1 and the other for line2.  The first task works fine, however the second fails with:

A first chance exception of type 'NationalInstruments.DAQmx.DaqException' occurred in NationalInstruments.DAQmx.dll
Additional information: NI Platform Services: The specified resource is reserved. The operation could not be completed as specified.

Task Name: _unnamedTask<3>

Status Code: -50103

This is a little confusing to me.  If I understand correctly, it should be possible to use two different PFI lines at the same time without interfering?  I'm on a PCI-6731.