Hi Erik,
There was an issue with the 1.2 JDBC driver as described in SAP 1428134, but for SAP NetWeaver 7.4 you shouldn't have such problems since you should be using the JDBC driver 4.0.
Are you using self-generated certificate or do you have another certificate used for encryption?
Also, do you have the screenshot from SUM about this error? It can be an error in SUM also.
Best Regards,
Luis Darui