On startup after the from v4.74 to v4.80 MercuryI failed to load throwing a "No such file or directory" error. I tracked the problem down to the path to the certificate in the MercuryI section of mercury.ini file. The previous certificate was named "imapcert" which v4.80 obviously did not like. I run in a second Mercury instance in which I run MercuryS so I copied its newly created certificate, then modified the path in the .ini. My suggestion is to consider whether it would be feasible to allow access to the module GUI after encountering an error like "No such file or directory".
One other suggestion is to provide the ability to create a certificate from outside of the modules so as not to be dependent on a module starting up in order to create a certificate.