Box - Conversion Error - User Enters 6 Numbers In 6 Different Text Boxes - Displays The Larger Of Those 6 Numbers

I am making a program, where the user enters 6 numbers in 6 different text boxes, and it displays the larger of those 6 numbers. But I also want to make it where if the user enters a string value (like S for instance) in the text boxes, it gives an message and says "please enter the numbers again" and the user gets to enter the 6 numbers again. But when I do try to do that, it gives an error message saying conversion from "w/e the user entered" to Double is not valid. If the user just enters the numbers, it works fine. However, I am trying to make it if the user does enter non numeric value, it gives a message window and the user can reenter the numbers again.

Here is my code Example

CODE:

This is where I am trying to use IsNumeric to show a message if a user does not enter a string so the user can renter the numbers again, but when the user does enter a string value (say in textbox 1) it gives me an error message saying conversion from "S" to 'double' is not valid.

CODE:

Then right here this is where I have my series of ifs statements, this part works fine, it displays the largest numbers of the 6 textboxes every time. Error free.

CODE:

And do this with variable number 2, 3, 4, 5.

I know there are easier ways to do these with arrays and stuff. But I am not there yet. I am still learning about ifs and stuff.