First, I would note that your function is not really a function... it does not return anything. On top of that, there is a problem of syntax with the line of code inside your function. There are two possible ways to call a subroutine...
Call YourSubroutineName(ArgumentList)
YourSubroutineName ArgumentList
The first method (using the Call keyword) requires the parentheses around the argument list... the second method should not put parentheses around the argument list. I know, people use parentheses all the time with the second method, but in each case I guarantee there is only a single argument for the subroutine. If you have a subroutine with a single argument and type it this way...
YourSubroutineName(SingleArgument)
if you look carefully, you will see VBA inserts a space between the subroutine name and that single argument in parentheses (virtually turning it into the second method's structure). Now, about those parentheses. Whenever you place parentheses that are not required by syntax, VB sees that as a signal to evaluate whatever is within the parentheses. For a single argument in parentheses, VB simply evaluates this as the argument itself... so, no problem. However, if you encase two or more argument values in parentheses, VB does not know what to do with it... using a numeric example, (2,3) cannot be evaluated because VB is not being told what to do with those two values. That is the problem with your code line inside your "function"... it contains two argument values inside parentheses that are not required by syntax, hence, an error is generated (you get the missing equal sign message because as you wrote it, it looks like a function call that is not returning a value anywhere (the value VB thinks the syntax should be generating is not being assigned to anything).