Why am I getting an error on my Schedule C, saying AMT Special Depr Allow must be entered?

If you took special (bonus) depreciation on assets you purchased for your business, then the alternative minimum tax (AMT) depreciation for those items may be different from the special depreciaton allowance you took. If you used TurboTax to prepare your tax return in previous years, then the AMT depreciation would be calculated and applied automatically to your return. If not, you may be able to see the AMT depreciation on the AMT version of Form 4562 in the prior year tax return and you would find the special depreciaiton amount in Part II. Otherwise, the default answer would be that the AMT special depreciaton would be the same as  the normal special depreciation, since it usually is.

Thank you for your explanation, but I’ve never done any of these types of depreciations for my business so they still don't make sense at all. I just put zero because it didn’t apply to me. Does that work?

Yes, if you never took any accelerated depreciation that would work.