function problem

I there, I don't know what is happening. I can't run any of my functions. I
can make but i can't run it. but I can run my trigger functions. what might
be the problem, bad installation??

I run this example function

CREATE FUNCTION add_one (integer) RETURNS INTEGER AS '
     BEGIN
         RETURN $1 + 1;
     END;
' LANGUAGE 'plpgsql';

and when I run add_one(2) i get this error

ERROR:  syntax error at or near "add_one" at character 1
LINE 1: add_one(int 1);

can you help please!thanks in advance

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