I appreciate what you are saying but there has to be a cause for what is happening. I have worked with hundreds of people that have used it with no problems so like I said, either it is something you are doing or it is a bad unit. Either way, i would like to get you squared away.
Let me give you an example. In last years Primal quest race all units were set to SPOT Cast or Track mode. We had a couple of units that were not showing up on the map. We found the teams and determined that the responsable team member had let the unit slide down the pack strap either to the rear or down the front. In another case a team was crashed out asleep on the side of the trail with their packs still on. The problem with this is that the antennae sits directly under the logo and has to be facing up with an unobstructed view of the sky. Once we moved the units back to the top of the shoulder while they were walking/running the units registered perfectly. The antennaes are that sensitive.
Here is another. Some people will do just like you described. They set the unit up in a good area facing up, turn the unit on and give it plenty of time to "warm up" and then hit the Check OK button. Here is the rub, the unit can take up to 20 minutes to transmit the message and if you aren't watching the unit every second you might not see the Message LED stay lit for 5 seconds (which indicates that the message is actually being sent) you might assume that it has already gone out and turn the unit off prematurely.
The fix is to leave the unit on for the full twenty minutes after sending the message. I know, that is a pain in the neck. We changed this in the new SPOT II. Now a dedicated message sent LED lights up after the message is sent. Much better.
I am betting that you are shutting the unit off too soon after sending the message. Try doing it the same way you have been doing it but let the unit stay on for the full 20 minutes after sending the message. Remember that this small, lightweight device that runs on two AA batteries has to do a very big job. It has to communicate with a set of navigation satellites that are a couple hundred miles above earth to get a good fix then communicate with a second separate set of communications satellites that are even farther up all while everything is hurtling through space at 25,000 mph. It is truly rocket science.
Give it a shot and see if it works. If not, send me a PM and I will see what I can do for you.
Wade
www.HardcoreOutdoor.com