RS232 communications can be adversely affected in a number of different ways. Below are listed a few things to inspect if instrument and software fail to interface correctly. As with any trouble-shooting scenario, all other applications should be closed to minimize the number of things that might be responsible for the situation. When communications is restored, begin to add back in these other items in an effort to identify the culprit.
Palm Pilots (and other such devices - scanners, cameras, serial printers, etc.)
Palms and their kin generally interface either serially (RS232) or through the USB (Universal Serial Bus). It is the nature of serial communications that only ONE software application can access a given serial interface port. That said, Palms are often the cause of communications failure. If in doubt, turn off the Palm receiver - often shown in the computer's system tray.
These devices too are serial. They initialize when the computer is booted and then hog the resources so that other serial devices are likely to fail. Solutions vary:  disable the device using the "Windows Device Manager",  remove the modem entirely if it is on a plug-in board,  modify the modem's IRQ (Interrupt Request) number or its COM setting (COM1, COM2, COM3, etc.),  see if the modem can be turned off in BIOS or though some software utility.
Virus Scanning Software
In theory, there should be no conflicts here - practically this is not always true. Poorly written software can block interrupt processing (virtually all serial communications is processed via the IRQ methodology) long enough so that all or part of the serial data stream is lost. The loss of a single character may be sufficient to break the connection.
Rarely, a computer ships with the RS232 ports disabled in system BIOS. It is beyond the scope of this page to detail the dozens of different BIOS programs. That said, if all else has been tried, this is indeed another element to inspect and remove from the suspect list.
Wires break. If a schematic and a multi-meter are handy, check the cable for continuity on all connected lines. Lacking these tools, try a second cable.
Missing or Out-of-Date Drivers
Each type of X-Rite instrument is independently supported by a unique driver. These are stored in a folder named "C:\Program Files\Common Files\X-Rite". Ensure that a driver matching the X-Rite instrument exists in this location. If not, or if there is reason to believe that the file is out-of-date, contact X-Rite at CASupport@xrite.com and request a more recent version.