I played around with this a bit more this morning (actually quite a long time!), and finally got it working. I did try out the data dumper (thanks for that suggestion) although I'm not sure it gave me anything useful. I changed this line: 
foreach $uid (keys %{$systems{$sys}}){

[download]
to this: 
@userids=keys %{$systems{$sys}};
foreach $uid (@userids){

[download]
and after that it all worked smoothly again. Does anyone know what this is any different?

In reply to Re: Use of freed value in iteration by js1
in thread Use of freed value in iteration by js1

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