gjpitt has provided this useful info for PDA users
Anyone who uses as PDA (Pocket computer) might have Microsoft ActiveSync installed on their machine. In itself this is not a problem. However, I found that ticking the box to allow serial/InfraRed communication will lock out the Com port. EVEN if the PDA is not connected and ActiveSynch is lying around inactive in the task bar.Unchecking the box in ActiveSynch allows WeatherDisplay to regain control of the com port.
Please note that this error may not be apparent at first when installing ActiveSynch especially for those of us who run WD 24/7. It only throws the error on re-boot.