If you're talking about syntax errors,
you should know that every JSP is translated into a
servlet before being compiled to a .class file. So, it is possible that a JSP file containing only 89 lines will give a syntax error at line 123. The solution ? Go find the corresponding servlet (myJSP.jsp will be translated into myJSP_jsp.java) and look at line 123.
If on the other hand you're talking about logical errors (the JSP file does compile and is shown but does someting unexpected), you could use the Log4J classes. A very good introduction can be found at
http://www.vipan.com/htdocs/log4jhelp.html.