sub loadEttx($){
    ...
    $self=>{ettx} = $xml->XMLin(shift);
}

sub loadTemplate($){
    ...
    $self=>{template} = $xml->XMLin(shift);
}
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The error pointed out by BrowserUk is actually present twice in the posted code (AFAICS).

In addition, there's no point in prototyping all the methods: prototypes are ignored in method calls. (The general monastic wisdom is: Just don't ever bother with prototypes unless you really know what they do and why you need one in a particular case!)

Update: The methods in the OPed code are prototyped to take either zero or one, or else exactly one, scalar arguments – but all three methods take two arguments! Again, it doesn't matter because no prototype checking is ever done.