This usually indicates that the certificate used to sign the AIR install has expired. Based on an archived discussion on this topic, you can search for SignatureTimeStamp in the signatures.xml file in the META-INF folder and, if it is not found, then the install has no signature time stamp and will not install after the certificate expires.
I'm having the same problem, but searching for SignatureTimeStamp is found. The search returns the following:
| <xades:SignatureTimeStamp> |
So, it would appear that there is a Time Stamp for the Signature in my case so the install should not fail. I would first check the above. Since you cannot install the app, you can try to open up the installation file with the .air extension as a zip file and drill down until you find META-INF and then drill down to find signatures.xml. Search for SignatureTimeStamp and see if it is found.
In the meantime, I was wondering if anyone else in this forum can explain why the install fails for me even though I can locate <xades: SignatureTimeStamp> in the signatures.xml file in the AIR install file.