#VALUE! error - why?

In my attachment, the Yearly tab represent data I get from an outside source, which I copy into my workbook. I take the yearly data (pcs) and divide it out into monthly buckets on the Monthly tab based on how many working days and weeks are within each month. This monthly data is then linked to many sheets within my workbook (only 1 sheet called Equipment shown in this workbook example). I get a #VALUE! error on the Equipment tab and can't figure out what is the cause. I can change the monthly formulas on the Equipment tab from =Monthly!B12/1000 to =sum(Monthly!B12)/1000 and the error goes away but I would like to understand what is causing the error.

Thank you in advance for any support.

You formula in sheet Equipment refers to an empty cell. K11 is empty

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K11 is supposed to be empty based on the formula within K11. Cells B11:Y12 populate data by month only if the start date of the product within the time frame.