This custom function replicates the list you have to go to in FileMaker Help to interpret what an error code means.
I parsed it from a page on the FileMaker.com support site. It's updated through v.15.
Start your custom function using the image below. The function definition is very long and is in the attached plain-text file, "ErrorDefinition function.txt".
ErrorDefinition ( 1634 )
A certificate verification error occurred. (new to FileMaker Pro 15)