Overflow Error - Solving Temperature using Antoine Equation

I am trying to calculate the temperature for the hdrogentation column that has a pressure of 515 psia. When I enter this value I get "Overflow Error 6". I defined P as Long, but I still get the same error. I know the code will work if the pressure is changed to 55 psia. I believe the problem may be due to a very long mmHg value, because 515 psia = 26632 mmHg while 55 psi = 2844 mmHg. I have checked the Antoine coefficients and they are correct.

Here is my code. Please help. Attached file also.

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I unwound your code a little:

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I suggest you step through it and see where the problem occurs. You might spend some time reading http://www.cpearson.com/excel/debug.htm