There are numerous possibilities for a low pressure alarm, to narrow the search consider your system as three parts: The waveguide, the dehydrator, and the interconnecting tubing. Isolating the dehydrator from the other two parts will determine if the problem is in the dehydrator.
Disconnect the outlet tube from the dehydrator and plug the output of the dehydrator. Turn on the dehydrator and allow it to build pressure. You can monitor the pressure via the web-based interface on the status page.
The NETCOM is pressure tested at the factory at 7.5 psi and is allowed a maximum leak rate of .040 psi / min. That translates to a 1 psi drop every 25 minutes.
If your leak rate is greater than this consult the ADH Netcom manual. Click here for more information about the ADHNetcom Dehydrator including manuals. There is a troubleshooting guide on page 43 of the manual.