Actually I want to perform the task in which if i select vale = this month from the pick list field Named " Status" and when i select date from the field named "Approval Date" then the month & year which is formula filed should print the same month and year and if select (next month) then month & year populated to +1 month and year +1 when onth is december... like same if i select (Nect to next month) the month & year field populated to +2 month .... below is the code which tried... it works well for conditon( THIS MONTH and NEXT MONTH) but i am facing problem in NEXT TO NEXT MONTH in the month of october november and december... plz help

IF(ISPICKVAL( Status__c ,"This Month"),
 CASE( MONTH( Approval_Date__c ) ,
1, "January"&" "&TEXT(YEAR( Approval_Date__c )), 
2, "February"&" "&TEXT(YEAR( Approval_Date__c )),
3, "March"&" "&TEXT(YEAR( Approval_Date__c )),
4, "April"&" "&TEXT(YEAR( Approval_Date__c )),
5, "May"&" "&TEXT(YEAR( Approval_Date__c )),
6, "June"&" "&TEXT(YEAR( Approval_Date__c )),
7, "July"&" "&TEXT(YEAR( Approval_Date__c )),
8, "August"&" "&TEXT(YEAR( Approval_Date__c )),
9, "September"&" "&TEXT(YEAR( Approval_Date__c )),
10, "October"&" "&TEXT(YEAR( Approval_Date__c )),
11, "November"&" "&TEXT(YEAR( Approval_Date__c )),
12, "December"&" "&TEXT(YEAR( Approval_Date__c )),"none"),

IF(ISPICKVAL( Status__c ,"Next Month"),
 CASE( MONTH( Approval_Date__c )+1,
1, "January"&" "&TEXT(YEAR( Approval_Date__c )), 
2, "February"&" "&TEXT(YEAR( Approval_Date__c )),
3, "March"&" "&TEXT(YEAR( Approval_Date__c )),
4, "April"&" "&TEXT(YEAR( Approval_Date__c )),
5, "May"&" "&TEXT(YEAR( Approval_Date__c )),
6, "June"&" "&TEXT(YEAR( Approval_Date__c )),
7, "July"&" "&TEXT(YEAR( Approval_Date__c )),
8, "August"&" "&TEXT(YEAR( Approval_Date__c )),
9, "September"&" "&TEXT(YEAR( Approval_Date__c )),
10, "October"&" "&TEXT(YEAR( Approval_Date__c )),
11, "November"&" "&TEXT(YEAR( Approval_Date__c )),
12, "December","January"&" "&TEXT(YEAR( Approval_Date__c )+1)) ,

IF(ISPICKVAL( Status__c ,"Next to Next Month"),
 CASE( MONTH( Approval_Date__c )+2,
1, "January"&" "&TEXT(YEAR( Approval_Date__c )), 
2, "February"&" "&TEXT(YEAR( Approval_Date__c )),
3, "March"&" "&TEXT(YEAR( Approval_Date__c )),
4, "April"&" "&TEXT(YEAR( Approval_Date__c )),
5, "May"&" "&TEXT(YEAR( Approval_Date__c )),
6, "June"&" "&TEXT(YEAR( Approval_Date__c )),
7, "July"&" "&TEXT(YEAR( Approval_Date__c )),
8, "August"&" "&TEXT(YEAR( Approval_Date__c )),
9, "September"&" "&TEXT(YEAR( Approval_Date__c )),
10, "October"&" "&TEXT(YEAR( Approval_Date__c )),
11, "November"&" "&TEXT(YEAR( Approval_Date__c )+1)+
CASE( MONTH( Approval_Date__c ),
12,"jan","feb"&" "&TEXT(YEAR( Approval_Date__c )+1))) ,null)))

 Error: Incorrect number of parameters for function 'CASE()'. Expected 22, received 23