It's not clear from the screenshot what full command you used. I am assuming the following:
java -cp smpp.jar:smpptest.jar:smscsim.jar com.logica.smpp.test.SMPPTest
Since you are on Windows, semicolon (;) is the correct jar file separator, not colon (:) which works on Linux.
So, the correct command is:
java -cp smpp.jar;smpptest.jar;smscsim.jar com.logica.smpp.test.SMPPTest