That's a problem with the CGI.pm that comes with AS 5.6.1. Try to upgrade it from CPAN.

In AS 5.8.0, it reads:

($param,$value) = split('=',$_,2);
next unless defined $param;  # skip - no error !
next if $NO_UNDEF_PARAMS and not defined $value;
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While in AS 5.6.1 it reads:

($param,$value) = split('=',$_,2);
$value = '' unless defined $value;
$param = unescape($param);  # "uninitialized" error !
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You're getting a blank name/value pair. The general format of an HTTP get request is

url?name1=value1&name2=value2&name3=value3
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CGI.pm is probably first splitting the query string on & chars, and then subsequently splitting those chunks on = chars, and associating each of those two pieces as the name and value of a key in a hash. If you put an & char at the start of the query string, CGI.pm is going to get confused, as it'll have an empty string that it tries to split in an = char, and then it will try to stick those values (that it didn't get) into a hash.

is there a particular reason you can't use a URL like the following?

choosecat.cgi?category=1
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I'm not trying to do that. I discovered this problem while testing the pages. I will go ahead and try a CPAN upgrade. Thanks, everyone, for your input.