I give up... a simples sum is turning out to be too much for me...

I have six sheets named by the weekdays (monday to saturday)

On cel E1 I have the day and month jun-16
On cell C68 I have a formula that either returns a number or
"" (empty)

I am trying to sum the C68 cells of the six sheets only if the month
of each sheet matches current month
(month(monday!E1)=6 for ie.

If one of the C68 cell is empty ("") then I get a #value error and I
cant seem to convert it to zero.


I know it is simple but I cant find the solution.
Please help...