Troubleshoot

Program runs OK in PC mode (directly from Small Basic) but won't compile to the brick using Explorer

There are a number of additional programming rules that have to be respected in order for Explorer's compiler to be able to compile your program to the brick (i.e. convert it into the RBF format that the brick understands, and then download it to the brick). See this page to read about these additional rules.

Program freezes or does not work as expected

In my experience the EV3 may not behave as expected if you are running it on battery power with a less-than-full charge. As soon as the battery energy indicator starts to drop down from the 'full' indication there is a risk that the motors may not move as expected. Keep the charger connected if possible.
Another thing to check is that you have plugged your motors and sensors into the correct ports. This site adheres to the standard convention that sensors will be plugged in as follows: 1=touch, 2=gyro, 3=color, 4=infrared or ultrasonic
This site also adheres to the convention that if you are using a mobile robot with two powered wheels then those powered wheels will be connected to motor ports B and C. If your motors and sensors are not attached to the ports referred to in your program then Small Basic may freeze when you run the program.
If your robot's motors seem to be misbehaving it could be because you have not applied the brake properly. Assuming you want the brake to be applied after a motor movement, be sure to make the last argument of your Motor command equal to "True" (case does not matter). For example, if you set the last argument to "Trrue" or to 1 then the brake will not be applied and the motor will 'coast' in an unpredictable way.
During the hundreds of hours that I have been working with EV3 Basic I have sometimes (maybe 3 times) not been able to get the expected behavior without reinstalling the firmware on the brick. This doesn't take very long, once you've realised it may be necessary, but you need to be aware that it is conceivable that using EV3 Basic could eventually corrupt the firmware in the brick. If you do need to reinstall the firmware, be aware that you will lose all your personal files on the brick, including all your programs.

Program won't run

The most common reason for this is that a program such as 'port view' or a settings dialog such as a WiFi dialog is open on the brick. In this case EV3 Basic programs cannot be run from either Small Basic or EV3 Explorer.

Program stops early or 'misbehaves' while using a wireless connection

If you have a wireless connection and run the program in PC mode (directly from Small Basic) then a significant amount of data traffic may occur between the PC and the brick while the program is running. A momentary interruption to the wireless connection could cause the program to misbehave or could cause the program to end prematurely. If you run the program in brick mode you are less likely to experience such problems. A program can be run in brick mode either using 'Compile and Run' in EV3 Explorer or first using 'Compile' in EV3 Explorer and then running the program from the brick's menus. Don't forget that not all programs that work in PC mode will work unmodified in brick mode because there are additional coding rules to be followed when writing code for use in 'brick mode'.
Other ways to reduce the likelihood of errors occurring while using a wireless connection would be to bring the robot closer to the PC (Bluetooth) or the router (WiFi) or use a wired connection between the router and the PC when using WiFi on the brick.

You use AVG Antivirus and find that it interferes with the launching of your Small Basic or EV3 Basic programs?

Try this solution, but be aware that it will slightly reduce the level of protection of your computer:

AVG > Antivirus Free > Menu > Settings > General > Turn off 'Enable CyberCapture'

Problem establishing a Bluetooth connection

If you have already established a Bluetooth connection for use with the standard Lego software (EV3-G) then the connection should be ready to use with EV3 Basic (recall that the standard software must be closed before you attempt to use EV3 Basic). If you have successfully paired the EV3 and your PC and have since then experienced a connection problem, try unpairing them and then re-pairing them. Here is the Bluetooth Settings panel in Windows 10 (I clicked the EV3 icon to show the 'Remove Device' (unpair) button:

Robot behaves erratically while using WiFi and EV3 Explorer after the WiFi connection was interrupted

There may be a bug that will cause erratic behaviour in this rather specific situation. See this page. You can reduce the chances of experiencing this problem by using Bluetooth rather than WiFi and, if you have to use WiFi, set the shut-down time to 60 minutes rather than 30 in the brick's settings menu so there is less risk that the brick will shut down while connected to Explorer by WiFi.

The motor was supposed to go backwards, but went forwards

This problem is probably caused by you giving a negative angle to the function, rather than a negative speed or power. Small Basic ignores negative signs in the angle argument, so if you want a motor to go backwards you must give the function a negative speed or power.

In EV3 Explorer, I can't delete a folder on the brick

You can only delete the current folder when all its contents have been deleted first.

The brick has frozen - will not respond at all.

Hold down the back, left and center buttons for a few seconds until the screen goes blank, then release the back button. When you see 'Starting' release the other two buttons. This procedure will not erase your programs. See this YouTube video.