4.6 is a very very old copy of Photopost hense we always suggest to upgrade and it is not off topic to suggest it.
Now as Michael already posted the only thing ever posted about zlib is you can not run it twice when loading a vb
header or you shall see undesired effects. Other than that we have never encountered such a thing.
I cant say whether your hacks are causing this or not but it is something you should look at. You should install a unhacked copy to see if you can replicate this.