I have built 2 applications: 1 forms app and 1 service app which talk to each other.

Problem I’m running into now is when I try to install them from sdb (or .NET) on a real device.  I am able to install either the forms app OR the service app, but not both.  It doesn’t matter which app I install first, I get the following error message, when installing the second one:

processing result : Register application error [-21] failed

Does anyone have any idea what this means and how to fix it?