If enabling Interrupts is causing the LCD to misbehave then...

Is outputing to the LCD actually causing an interrupt?... ie have you connected the LCD to a pin that might itself be triggering an interrupt, and check your PIC that your LCD connections have not been bridged across to an adjacent pin that might be triggering an interrupt.

Try to enable interrupts one by one to see which one (or which ones) are causing the problem. This might give you a clue where to look further.