error I/O connection

I have a web system with java 1.5, tomcat 5.5, sql server 2003, it works but when there is a data base access it takes a long time !
and after a few minutes I receive this error

Code:

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ERROR:: Servlet.service()
javax.servlet.ServletException: java.sql.SQLException: I/O Error: Connection reset
at net.sourceforge.jtds.jdbc.TdsCore.nextToken(TdsCor e.java:2277)
at net.sourceforge.jtds.jdbc.TdsCore.login(TdsCore.ja va:599)
at net.sourceforge.jtds.jdbc.ConnectionJDBC2.<init>(C onnectionJDBC2.java:331)
at net.sourceforge.jtds.jdbc.ConnectionJDBC3.<init>(C onnectionJDBC3.java:50)
at net.sourceforge.jtds.jdbc.Driver.connect(Driver.ja va:178)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)

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any ideas?

Do you work with servlet?
If yo work with servlet, did you include servlet.jar in the classpath?
check line 227, there is the error.