All add-ons must have a resource named 'MDID' with a resource ID of 32500. This resource defines the unique ID of the add-on.
The 'MDID' is composed from two parts:

• Developer ID: the ID of the developer, given by GRAPHISOFT after a successfull registration.
• Local ID: the ID of the add-on, generated by the developer after creating a new add-on at the profile settings.

If your add-on has invalid 'MDID', then ARCHICAD will refuse to load it. If two add-ons have identical 'MDID' resources, then in order to avoid collisions ARCHICAD will refuse to load those. So make sure you generated new identifiers for all of your add-ons!

As it does not require localization, the 'MDID' resource should be contained by the Fix.grc.
Simply copy the two identifiers (highlighted on the picture above) into the grc file:

'MDID' 32500 "Add-On Identifier" {
    628121456
    719857724
}

If you have any further questions, do not hesitate to ask them at archicadapi@graphisoft.com!