For those who use Tomcat with Bitronix, this will fix the problem:
The error indicates that no handler could be found for your datasource 'jdbc/mydb', so you'll need to make sure your tomcat server refers to your bitronix configuration files as needed.
In case you're using btm-config.properties and resources.properties files to configure the datasource, specify these two JVM arguments in tomcat:
(if you already used them, make sure your references are correct):
e.g.
-Dbtm.root="C:\Program Files\Apache Software Foundation\Tomcat 7.0.59"
-Dbitronix.tm.configuration="C:\Program Files\Apache Software Foundation\Tomcat 7.0.59\conf\btm-config.properties"
Now, restart your server and check the log.