Linux Mint guest hangs when serial ports enabled

[TFO]

I've got a Linux Mint guest (Windows 7 host) and have mapped host serial ports COM1 and COM2 as host devices. I have the latest version of VirtualBox as well as the guest additions. A few days ago the Linux guest hung and I had to cycle power to get back to Windows. Now every time I try to bring up the Linux guest with serial ports enabled it hangs. If I disable the serial ports it seems to work fine. Unfortunately we need the serial ports to interface with our calibration equipment. Any ideas on what might be going on? Thanks.

[TFO]

I have found conflicting documentation on how to set up serial ports as host devices. Some documents say to use COM1 as the path, others say use COM1: (colon has some significance?) others say to enter /dev/ttyS0 (this doesn't seem to work because VB converts to \dev\ttyS0 which isn't even a legal path)

Does anyone have insights on how to correctly set up a Windows serial port as a host device on a Linux guest?