Hi,
Sometimes what you are experiencing is indeed a Prometric web site issue. Please not that other times it just means that the testing center that you have chosen does not have any availability in the time frame that you were looking for. I do most of
my testing in Massachusetts and most of the testing centers near me do not seem to offer the Microsoft exams that I am looking for when I want to take them.
You might want to try some other days for the same testing center just to see if there is any availability. That will help rule out web issues.
Please do not forget to click “Vote as Helpful” if any post helps you and "Mark as Answer”if it solves the issue.