In AX EP there are times when unexpected errors are appearing. One of them is "An unspecified runtime engine error has occurred. Error code: %d.".
Cause: not sure. I believe as the message says it has to do with the process space of the AX EP ...
Fix: well, if you'd expected something else except the following (which doesn't work for you), just send a reply ... love to hear other scenarios; the fix is a simple AOS and IIS restart, and things should work.