Wow, this is a cutting-edge error, and the ora-12528 is brand-new with 10g.
The docs note:
ORA-12528: TNS:listener: all appropriate instances are blocking new connections
Cause: All instances supporting the service requested by the client reported that they were blocking the new connections. This condition may be temporary, such as at instance startup.
Action: Attempt the connection again. If error persists, then contact the administrator to check the status of the instances.
See here: http://www.dba-oracle.com/sf_ora_12528_tns...on_tips_bc1.htm
Brian Peasland notes: "This is a known problem with Oracle 10g where a SHUTDOWN IMMEDIATE is followed by a STARTUP MOUNT."
Try bouncing the instance and try again . . .