Error "uasort()" in installing eCommerce 5.x-4.0-alpha3

Hi,

When i'm installing eCommerce 5.x-4.0-alpha3 (i click on the "Store" sub-module and i valid this), i have the following error message :

uasort() [function.uasort]: Invalid comparison function. in /Volumes/TRAVAIL/clients/drupal/sites/all/modules/ecommerce/ec_receipt/ec_receipt.module on line 519.

Somebody knows why i have this issue ?

Thanks,
Julien.