It could be a typo in the SYNOPSYS section of the POD. I have never used this module, but looking at its Perl source code is pretty simple. I searched for the string "no alias for" (your error message) inside http://cpansearch.perl.org/src/SMCKAY/Bio-PrimerDesigner-0.05/lib/Bio/PrimerDesigner/primer3.pm, which checks the %aliases hash. It seems like PRIMER_PRODUCT_SIZE is not a key of this hash.

If you agree, you should create a minimal testcase to reproduce the problem and Report a bug on the Bio::PrimerDesigner webpage.

Update: After another quick look, maybe it should be PRIMER_PRODUCT_SIZE_RANGE.