You can sometimes encounter this type of error popup
This popup notices you of a fatal error that occured within the code without a proper way to handle it. Such errors are called Exceptions. An exception can be caught and handled to prevent the game from crashing or reaching a broken state. Some errors are fatal anyway and are often not dealt with (because there is no good way to do so). Those Uncaught Exception then trigger an error popup so we have at least some information regarding what caused it and the code involved. Here is a summary of the popup content :
The error description gives you info about the type of error (most common is Null Access for instance). The callstack gives info about the path the code took before encountering the error. Sometimes it is not relevant or helpful, but these info are always best shared with the devs & customer support. When referring to the error, use the error description rather than the too generic "uncaught exception" name.