Excel = Formula Showing as 0.00

I have a users who has a spreadsheet and is trying to do a simple function of copying the data displayed earlier in the sheet towards the bottom of the sheet.

R66 forumla - =ROUND(SUM(R17:R19)+R23+R46+R49+R52+R65,5)

R100: =R66

R66 calculates properly but R100 only shows 0.00 regardless of how I format it. Shouldn't it show the whatever number the formula in R66 comes up with? My user is using Excel 2010.

Is the result of the formula in cell R66 something like '0.00000000012' ?
It looks like cell R100 should just show the result of the formula in R66.

No. It's showing a number (70,530.90 to be specific). Formatting for that cell is Number, 1000 separator, 2 decimal places, (1,234.10) in red

Cant think of anything wrong with the formula in cell R100.

Only thing i can think of is that the workbook is set to calculate options manually. You can check this in Excel 2013 by going to: Formula's - Calculate now (on the top right, or press F9). Does this help?

I've tried that as well and still nothing. It's extremely frustrating and its a pretty simple function.

Looks like there were some circular reference in the sheet. Correcting those fixed it.