You should also end the each of create statements with a GO or semicolon:

Also, should add the schema to the function. For example the below uses the dbo. schema:

CREATE FUNCTION dbo.CalculateDistance
            (@Longitude1 Decimal(8,5),
            @Latitude1   Decimal(8,5),
            @Longitude2  Decimal(8,5),
            @Latitude2   Decimal(8,5))
        Returns Float
        AS BEGIN
        Declare @Temp Float

        Set @Temp = sin(@Latitude1/57.2957795130823) * sin(@Latitude2/57.2957795130823) + cos(@Latitude1/57.2957795130823) * cos(@Latitude2/57.2957795130823) * cos(@Longitude2/57.2957795130823 - @Longitude1/57.2957795130823)

        if @Temp > 1
            Set @Temp = 1
        Else If @Temp < -1
            Set @Temp = -1

        Return (3958.75586574 * acos(@Temp) )

        End
        GO

See SQL Fiddle with Demo

You should also end the each of create statements with a GO or semicolon:

Also, should add the schema to the function. For example the below uses the dbo. schema:

CREATE FUNCTION dbo.CalculateDistance
            (@Longitude1 Decimal(8,5),
            @Latitude1   Decimal(8,5),
            @Longitude2  Decimal(8,5),
            @Latitude2   Decimal(8,5))
        Returns Float
        AS BEGIN
        Declare @Temp Float

        Set @Temp = sin(@Latitude1/57.2957795130823) * sin(@Latitude2/57.2957795130823) + cos(@Latitude1/57.2957795130823) * cos(@Latitude2/57.2957795130823) * cos(@Longitude2/57.2957795130823 - @Longitude1/57.2957795130823)

        if @Temp > 1
            Set @Temp = 1
        Else If @Temp < -1
            Set @Temp = -1

        Return (3958.75586574 * acos(@Temp) )

        End
        GO

See SQL Fiddle with Demo of all functions being created.