SignagePlayer keeps on looping in “Please wait…”

The Cache is the problem there, you will need to clear cookies and cache so that the passwords and registered settings will be cleared.

Close player

In XP
Delete C:\Documents and Settings\USER_NAME\Application Data\SignagePlayer.XXX
(USER_NAME = logged on windows XP user)

In Windows 7 / Vista
Delete C:\Users\USER_NAME\AppData\Roaming\SignagePlayer.XXX
To get to this folder,  Click on Start, and on the search field type %appdata% hit enter, and then delete the SignagePlayer.xxxx folder.

In Mac OS X
sudo -1
AND
rm -r -f /Users/YOUR_USER/Library/Preferences/SignagePlayer.XXX
AND
rm -r -f /private/var/root/Library/Prefer
Note: Hit tab after typing the first few letters of the path you want to type in to auto complete it. Mac has that feature in the terminal window.
and re-launch and re-register