couchdb filters and function_clause error

[toni]

i have a problem with couchdb filters. 

 $curl
'http://HOST/mydb/_changes?filter=app/important' 

the response i get is
the following error: 

 {"error": "unknown_error", "reason":
"function_clause"} 

and this is my very simple test filter doc: 

 {

"_id": "_design/app",
 "_rev": "4-51941e89602a03c3ccf3c62858b9051b",

"filters": {
 "important": "function(doc, req) { return false; }"
 }
 }


what´s wrong with this filter? 

all other views i created and tried are
working.