Rule of Thumb for all updates (from any source). I personally, always (as far as I can remember), get this error if I don't first uninstall the current version. I don't know if this is a software issue that enTourage can adjust, but I do think it's an Android thing (other users, like Cheyenne, can confirm/refute).

No harm in trying without uninstalling though

PS: Miss seeing you around more, Eddy