Re: Error instaling DB to ACTIVITI: "Cannot serialize session attribute..."
Can you give us a little bit more information about your configuration?
Based on the timing in your logs, I believe this is an issue with the JDBC connector. At 12:37, 24 & 25 seconds in the catalina log, you see:
mar 31, 2017 12:37:24 PM org.apache.catalina.startup.HostConfig undeploy INFORMAÇÕES: Undeploying context [/activiti-explorer] mar 31, 2017 12:37:25 PM org.apache.catalina.loader.WebappClassLoaderBase clearReferencesJdbc
Which is at exactly the same time that the localhost log is saying that your application is unable to serialize the object. Can you verify that your datasource is set appropriately the mysql database, and that you have the JDBC driver available?