I want to get the day count without weekend days.

I just tried this in my own org. I created a formula field returning a number and only changed Opportunity_Close_Date__c to one of my date fields and I get no error.

Here's my formula:

DATEVALUE(CreatedDate)- Date1__c
-
(
FLOOR((DATEVALUE(CreatedDate)   - Date1__c)/7)*2
+
IF(AND(WEEKDAY(Date1__c )=1, WEEKDAY(DATEVALUE(CreatedDate)  )<>7),1,
IF(CASE(WEEKDAY(Date1__c ),1,8,WEEKDAY(Date1__c ))>CASE(WEEKDAY(DATEVALUE(CreatedDate)  ),1,8,WEEKDAY(DATEVALUE(CreatedDate)  )),2,
IF(OR (WEEKDAY(DATEVALUE(CreatedDate)   )=7, WEEKDAY(Date1__c )=1),1,
IF(OR (WEEKDAY(DATEVALUE(CreatedDate)   )=1, WEEKDAY(Date1__c )=7),2,
0)))))

What data type is Opportunity_Close_Date__c ? Is it a date field?