While developing a small jsf application with datatable I am having following problem with this error
The method setVar(String) in the type DataTableTag is not a
Looks like you ran into this bug:
Bug 41912 - JSF datatable does not work on tomcat 6.0.9
Regarding the comments on this page a possible workaround would be changing the combination of server and/or jsf version.
Sounds like you're trying to send a String to a relational database when it's expecting another type, like Date or number, to a particular table and column.
HTTP form elements only know about Strings. You should be validating and binding values from the UI on the server side before persisting them in a database.