It is really not the holding down the mouse wheel. It is the middle mouse button that needs to be pressed. Depending on some models of mice you can change what that function is when you press down the mouse wheel. Be sure that it is set to the 3rd button (middle mouse button) for a mouse. I know that my Logitech mouse has some issues when I press the middle mouse button (mouse wheel). It doesn't always register that I pressed the middle mouse button.
To sum up... it might be a hardware problem.