JDBC :: No Suitable Driver Found For Oracle Database Connection

I have small Java code, which execute every day and checks for data in database using Cronj Schedular and everything works fine, but recently I have observed that, it is failing due to
  
    java.sql.SQLException: No suitable driver found for jdbc:oracle:thin:@160.110.xx.xxx:1521/test
 
At the same time, when I run my test code to check Database connectivity that works fine without above exception. I'm unable to figure it out. Although, there was just slight code change, but that was nowhere related to Database or Database connection.  
 
dbconf.java
    public class dbconf {
    private Connection connect;
    private String connstr;
    public Connection getConnection() throws SQLException {
    connstr = "jdbc:oracle:thin:@160.110.xx.xxx:1521/test";

[Code] .... 
 
Application Log file
 
    Wed Jul 01 09:25:17 IST 2015:------- Initializing -------------------
    Wed Jul 01 09:25:17 IST 2015:------- Scheduling Jobs ----------------
    Wed Jul 01 09:25:17 IST 2015:------- Job Started Running ----------------
    Thu Jul 02 06:00:00 IST 2015 : Job Executed..!! Bschedularv2.2
    java.sql.SQLException: No suitable driver found for jdbc:oracle:thin:@160.xxx.67.xxx:1521/test
    Sat Jul 04 06:00:00 IST 2015 : Job Executed..!! Bschedularv2.2
    Sun Jul 05 06:00:00 IST 2015 : Job Executed..!! Bschedularv2.2
    java.sql.SQLException: No suitable driver found for jdbc:oracle:thin:@160.xxx.67.xxx:1521/test
 
So, you can see, It failed on 3rd of July and 5th July as well. But, in between it ran fine.