I've been struggling with this for the past two days and I have replicated this issue on 2.1 and 2.1.2. Both Fresh Installs.
I'm logged in as admin. Immediately after adding a second user and setting them to Administrator, the Write Post page will not completely load. If I change the second user's role to something other than administrator, the write post page will load successfully.
I'm running this on XAMPP, which is running MySQL 5.0.20-nt. PHP is 5.1.2.
Is there a work around to have multiple admins? This is for a group blog that we all need admin access.