For core 6 It is not a good idea to remove the square brackets, because Drupal will be unable to assign the dependancies.
Dependancies is a Drupal ARRAY that is why it needs the square brackets.

However, perhaps in core 5 the dependancies variable was not an array, in which case great spotting keyone !

The administration menus are built based on certain arrays, since you can navigate to admin/store/settings/uc_rss_feed then i guess the arrays are built ok.

As a first step check the permissions you have, are you allowed to administer this module? Are you logged in as UID 1?

You may be better off upgrading to core 6, it is easy.