Grasping at straws...

Do you have a package statement between the use Date::Calc and the call to Delta_Days?

Do you have warnings enabled?

Does this happen only in the debugger?

Did you manually move Calc.pm, instead of using Makefile.PL or ppm to install it correctly?

Does changing it to call Date::Calc::Delta_Days help?

What does this show (just before the Delta_Days call):

use Data::Dumper;
print STDOUT Dumper($syyyy,$smm,$sdd,$eyyyy,$emm,$edd);
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