"Not able to find 'count' function"

"Not able to find 'count' function"

I am trying to edit some code that is currently working but am not getting an error that says:

"Not able to find 'count' function"

The code with the problem is:

filecount = Purchase_Request_Form[ID == input.Request_ID].count(Build_Files.ID);


As I said this code is currently working including the count function.

Im trying to change a parameter in an if statement in this form and I cant save the updated code now because of this error. I am in free flow scripting mode.

What is wrong?