Hello Rio,
I believe that is not possible.
1) Metrics are stored in the Smartstor database.
2) Errors descriptions and traces are stored in the Traces database, see Query Stored Events - CA Application Performance Management - 10.5 - CA Technologies Documentation
You could try to use CLW to export the exception, see CLW Command Reference - CA Application Performance Management - 10.5 - CA Technologies Documentation
Here is an example:
java -Duser=Admin -Dpassword= -Dhost=localhost -Dport=5001 -Xms512m -Xmx512m -jar CLWorkstation.jar get historical events matching \"type:errorsnapshot AND time:[20170828 TO 20170829]\"
If you need a txt version, you can load the file using Query Historical Events window and then save the file as txt.
I hope this helps,
Regards,
Sergio