"Error opening zip (), need to handle this better..." ?

[Blastdown]

Error opening zip (Add-Ons/Script_HeadcrabZombie.zip), need to handle this better...
Error opening zip (Add-Ons/Vehicle_toboggan.zip), need to handle this better...

Just yesterday I had this same error with three print files that did not seem to have any visible problems(though I deleted them anyways just in case).

What does this mean?

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[Space Guy]

Try redownloading the Add-Ons or reinstalling Blockland.

[Ephialtes]

Essentially it means the zip is corrupted/badly formed and Blockland cannot read it normally.