Method 1. Settings manipulations and device restart.
The easiest way to fix the error is to restart Android smartphone. And it works just fine. However if there is no luck and the error message still bothers you, try to tackle it with settings change. To do so, go to appropriate menu section, turn on "Airplane mode" option, wait for 5-10 seconds for device restart, then turn off "Airplane mode" and check the result.
Method 2. Start device in Safe Mode.
It is possible that a recently installed app is caused "Connection problem or invalid MMI code" error message. You can check it by restarting your device in Safe Mode. To do so, follow the steps below:
- Turn off your phone;
- Press the power button. Press the volume button. Hold the volume button until Company Logo disappears and the message that the device has been restarted in Safe Mode successfully appears in the screen .
- Check whether the error has gone. If it is, you have to spend your time to find the app which caused the error and delete it.
- It is known that FX Camera application often causes "MMI code" error for Samsung smartphones.
Method 3. Modify prefix code.
This method is pretty easy despite the fact that it looks utterly preposterous. However many users report that it actually works. It is to add a coma to the request. For example, your request for checking your account balance will look like : *100#,. To add a come, you have to hold “*” button.
We will regard other reasons for "Connection problem or invalid mmi code" error to some connection issues. Nevertheless we present here a couple of ways to solve the problem. It could be done with Android smartphone settings manipulations.
Case 1. Low signal level.
If the signal level is low or unstable, your smartphone looks for a stronger signal. It changes constantly its network format such as 4G, 3G, WCDMA, EDGE. You can visually determine the cause of the issue. Looking at the screen you can watch Network Type Indicators are changing above signal level bar icon. Now what you have to do is to slow down the speed. Navigate "Settings" ->"More" -> "Wireless and Networks"-> "Mobile Networks: -> "Network Operator". Select 3G or even 2G.
Case 2. Alien roaming provider.
It is a common situation which a user don’t identify until he is sending a USSD code, that is, Android smartphone is setup for an alien provider. It is not a big deal. If you want to send USSD codes, just go to Settings, select manually your mobile operator from the presented networks. Still no luck? It is possible that your request is not supported in the area of your current position. Call provider upport service to clarify it.
Finally, the last and the most unfortunate case. The cause of the issue is a corrupted SIM-card. Probably it was cut off or reinserted many times. In any case the appearance of the overall card like much used and look old is not necessarily guarantee of internal micro fractures. Nevertheless it is a reason to change it for a new one before having connection problems at exactly wrong time.
You can see that "Connection problem or invalid mmi code" issue can be verified and fixed pretty easy. However you can always call free to provider’s technical support service instead of sending a USDD code. It’s up to you!