We received a support email today, but it bounced back from the user (Chiddu) so we thought we would post our reply as this is the first issue we have had around this reported. Our reply notes our experience:
What kind of error message did you get from the install? We have seen that some HTC devices do not download the file completely when an OTA (Over The Air) install is tried, seems to be an issue with Windows Mobile 6.5 or with the carrier. Could you download the current install file (http://www.universital.net/products/download/mailnotificationsetup.cab) on the PC and then copy over to the device and try the install? The file should be about 2 MB in size.