What is the "cost" of my entire home when calculating home office depreciation?

It would be the original price you paid for the house, plus any improvements you made to the house since buying it.  The original price is the contract price, regardless of the amount that was mortgaged or paid in cash.

I did this but during error check I got a message for Form 2106 stating that "Eligible Sec 179 property has unacceptable value".  What is the solution?

Watching as I had the same issues..

Have  similar issue - inherited a home.  I have my  property tax assessment  - - would it be the "Taxable Value", "Assessed Value" or something else?

It would be the Fair Market value of the property as of the date of death of the deceased.  If an estate return was filed, that value was estimated as part of the estate return, so you could take it from there.  Property tax assessments are rarely of any use in this determination because they are not as of the date of death.

The 179 property error message does not relate to the house value because the house itself is not eligible for a section 179 deduction. This error message is most likely stemming from an error in your entry of the cost of equipment of some kind or a car.