As haoess suggests, pseudohashes are causing the problem. However you may not have intended to create one: if you have inadvertently assigned an arrayref of a particular form to $hashref then I'd expect error messages along the lines you are seeing.

The solution: look back earlier in the code to where $hashref is set, and perhaps add some diagnostics around that point to find out why it isn't getting set to a hashref as you clearly expected.

This sort of problem is exactly why pseudohashes have now been deprecated, and will be removed in the next major release of perl.

Hugo