Ok, so in 0.4.5 I added in a security “feature” that would block people without proper security levels from seeing the admin pages. This was a temporary kludgy fix that is probably going to go away sooner rather than later.
The only problem was that it made the plugin a little too secure and blocked all users from using their new installs. This wasn’t a problem related to a specific version of WordPress, only fresh installs of Gigs Calendar 0.4.5. This new version should fix the problem for you and let you gig away happily.