Problems with searching 60 Fields for String and entering the number 10 into a "BSSB" field; No errors

There are at least two issues with your function. I'll post the code again in a more formatted way, so it's easier to refer to specific lines in it:

function SetBSMarksmanshipFieldValues() {
    for (var i = 1; i<61; i++) {
        var CSki = ("CSk" + );
        var CSkStringValue = this.getField(CSki).valueAsString;
        if (CSkStringValue.valueAsString == "Marksmanship")
            { this.getField("BSSB").value = 10; i = 60;}
    }
}

Line 6: Minor issue. That is not a good way of breaking out of a loop. Use the "break" command instead.

Line 5: Major issue: You've already defined CSkStringValue as the string value of the field, so there's no need to access this property once more.