Please post your code. Now I can only gues: perhaps you use a variable whose value is the 'abc' string as if it contained a hashref.

$ perl -e 'use strict; my $a = "abc"; $a->{"aaa"} = "a"'
Can't use string ("abc") as a HASH ref while "strict refs" in use at -
+e line 1.
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Here the variable $a contains the string, but in $a->{"aaa"} = "a" I used it as if it contained a hash reference.