Unable to open session to "ASRL4::INSTR"

[Double_D]

I have a LabVIEW application (in use for approximately 3 years) that is used to read environmental data from two transmitters.  Communication with these devices is through a Moxa serial server, which takes Ethernet data on the computer side and serial data on the instrument side.  The instruments are mapped to COM ports via the Moxa software.  I can only get one transmitter to work now. 

COM4 has the yellow exclamation point symbol in NI-MAX.  If I attempt to open a test session to the device, I get the message in the subject line along with "Return status code: 0xBFFF0000  Status name: VI_ERROR_SYSTEM_ERROR  Unknown system error (miscellaneous error)."  If I try to access the device through the Moxa terminal emulator, I get a message indicating that the port is occupied by another program.  I am unable to delete the resource in MAX (this option is grayed out).  I have tried restarting my machine, thinking that this might clear the conflict, but that had no effect.

I can communicate with the Moxa servers over ethernet with no problem (e.g., I can ping both devices).  The only difference I can think of between my current configuration and the "last known good" one is that I have upgraded LabVIEW from Version 7 to 8.5.1 (and changes to other NI components associated with that).

[RavensFan]

I've had no problems with serial devices nor heard of any with LV 8.5.  I'm actually installing 8.5.1 right now.

I would try reinstalling the device drivers for 8.5.1.  Perhaps there was some problem with the installation of NI-VISA.  I actually just had a problem when the device driver installer wanted disc 2.  It didn't find it right a way for some reason, then asked for disc 1 back in.  I did that.  Then it asked to continue, and actually skipped over a couple components because it couldn't find them on disc 1.  So I put disc 2 back in and the install picked up where it left off.  Don't know why it had a problem with disc 2 on the first attempt.  So I'm planning on trying to reinstall the drivers again once they are done.  Of course that is an hours long process.