It sounds like your original error might be in the included page, and that error message is being swallowed by the including page.
If checking a variable, are you using code like getSession().getAttribute( "name" )? If so, you might be getting an NPE ... you'd need to call getSession( true ).
Also, your useBean directives. Do you want to use class or type here? Maybe you're getting an instantiation exception on one of your beans?
Just wild guesses!