[Resolved] SQL2k Scope Problem

[yrwyddfa]

Morning, all. Got this problem and can't figure it out - must be missing something extremely simple. Here's the code:

create function IncAlpha
    -- Increments a single alpha character
    -- uses this sequence ABCDEF..Z
    (@Alpha char(1))
    returns char(1)
as
    begin
        
        declare @RetVal char(1)
    
        if @Alpha is null or @Alpha=''
            set @RetVal='A'
        else
            set @Retval= char(ascii(@Alpha)+1)
 
        return @Retval
 
    end
go

When I try to compile the function it raises an error on the 'return @Retval' line saying that I must declare it:

Server: Msg 137, Level 15, State 1, Procedure IncAlpha, Line 17
Must declare the variable '@Retval'.

What exactly am I doing wrong, here?