CA Schedule S Error: "Double Tax Amount-Other St must not be more than the double-taxed income taxable by California" Why won't it accept it when both values are equal?

Of which state are you a resident?  If you are a California resident, then please be aware that California and Virginia are reverse credit states.  With most states that do not have a reciprocal agreement, you are taxed in both the state you work in and the state you live in.  To reduce the effect of double-taxation, the state where you live will give you a credit for the tax you pay to the state you are working in (but no more than what your resident stated actually taxes the income).

In a reverse-credit arrangement, the opposite is true.  Your resident state taxes all of your income, and the nonresident state will provide you a credit for the tax you pay to the resident state.  So, if your state of residence is California, California will not allow you to claim a credit for your taxes paid to Virginia.  Rather, you will claim a credit on the Virginia return for the tax you pay to California.

Hopefully that explains the diagnostic, but if it does not, please feel free to comment additional clarifying information.