Error 1004 - Inserting value to a cell

I have seen some posts which looks a little bit like the issue I am having but it is not exacly the same. I do not have the code in front of me so I will try to be as clear as possible and post the code next tuesday.

My problem is that I have some checkboxes in Excel, when they are selected, a userform is shown and users can set a number a clic a "OK" button. After they hit "OK", the cell on the right of this checkbox is set to the value the user has entered in the userform. For the moment, it is working for rows 7 and 9 but once I get to rows 11 and further, I get : Error 1004 application define or object defined error which is thrown when trying to set the cell value. My concern is, why would it work for rows 7 and 9 but not the other ones? The format of the cell is the same nothing is different.

As I said, I will post the code on tuesday but here are some details : The checkboxes all have variable names with the same format : "ConformityE6" -> E6 representing the cell range. So for the checkbox in cell E11 I have : "ConformityE11" etc. The cell where the value needs to be entered also have variable names with this format : "nonConfE12"

If anyone has any idea what could create the problem it would be appreciated.