which version of qliksense are u using it? may be u can try to check the Port Number and host name. (IBM DB2 default Port number is 50000)
also check this steps,
use an ODBC connection... I couldn't use the Qlik IBM DB2 connector, had the same error messages.
install this on your machine https://www-03.ibm.com/systems/power/software/i/access/solutions.html
(maybe not the complete package, only the odbc drivers)
and set up ODBC connection that you will then be able to use in Qlik Sense