Why am I getting number 500 when choosing a plan?

[MatBaird]

I'm trying to chose a plan but all I'm getting is the number 500, can anyone help?

[StephensWorld]

You'll need to provide more details about the store/account (is this a trial account, or a development store? are you the store owner or a staff member?), where you're clicking (ie. how you're trying to choose a plan) and include screenshots of any issues. 

"All I'm getting is the number 500" -- isn't enough to try and help troubleshoot this.