Java game error is an application error and not a hardware error. So replacing the SIM card will never fix this problem. There's a possibility that the Java version that you have in your phone is not supported by the MXIT.
Verify the supported Java versions of MXIT. Then check the version of Java you have in your phone.
Try to upgrade the Java in your phone, then try to download the MXIT again. If same problem occur, try to download another application, and if it DOES work, then there's no problem with the phone. There could be a problem with the application (mxit) that you are trying to download.
Contacting the manufacturer for additional info is a good thing to do as well.
Answers & Comments
Java game error is an application error and not a hardware error. So replacing the SIM card will never fix this problem. There's a possibility that the Java version that you have in your phone is not supported by the MXIT.
Verify the supported Java versions of MXIT. Then check the version of Java you have in your phone.
Try to upgrade the Java in your phone, then try to download the MXIT again. If same problem occur, try to download another application, and if it DOES work, then there's no problem with the phone. There could be a problem with the application (mxit) that you are trying to download.
Contacting the manufacturer for additional info is a good thing to do as well.
Thank you and good luck!
Try again, sometimes MXit releases a new version that breaks it, but one of the older versions or latest version should work.