Hallo Stanley,

first you must analyze where the interference comes from and how it's manipulating functionality. So, first you must do some measuring with oscilloscope. It should be possible to fix your problem without the help of opto. If you have a poor ground rooting, you will again have problems, and again and again. You cannot insert optos all the time.

I think, that shielding, grounding and filtering will make your circuit work.

Kai