"This add-on cannot be validated. Please contact the distributor." error

[ReignBough]

I have this error on some units (PC). I know that this maybe caused by not having a correct MDID. I have the correct dev ID and MDID since it is okay on my working unit and other units too.

What are the other possible cause (and solution) to this error.

[dfintha]

Hello,

It is caused by failing the MDID validity check.
If you are sure the MDID is correct, check for possible file corruption.

Best regards,
Dénes

[Akos Somorjai · Accepted solution]

You can also check with Dependency Walker (assuming Windows see http://www.dependencywalker.com) to check if you have all the dependencies (DLLs) installed. The easiest way to do that is to copy the add-on beside ARCHICAD.exe, and open that copy in Dependency Walker.
On macOS the

otool -L [add-on-executable]

gives you a similar, though non-hierarchical list.

Best, Akos

[Ralph Wessel]

This message is the response to every possible error loading an add-on – it would be better worded as, "something went wrong loading the add-on".

I think Ákos is right in pointing you toward checking dependencies. If another DLL your add-on is linked against is missing or an incompatible version, the add-on won't load and you get this error.