#VALUE error after linking 2 documents

[ITuoh]

Hi all, I would be very appreciative of all responses to help,

I have linked one file to another with the help of a formula. I have been using both files simultaneously for the past weeks without any trouble. However, for some reason, the output for all the formulas I have already typed are now returning a #VALUE error. 
I have tried to change/update  the source of the referent file multiple times but I still get the same error everytime. What could be the problem/ what could I be doing wrong?

Thank in advance for your help.

[#2]

What's your formula?

[#3]

My formula was a combination of sum and countifs.
So basically, wanted to count the number of cell contents which matched a compound criteria.

[#4]

@ITuoh 

COUNTIFS() cannot access closed workbooks.