The Monitoring configuration for target out of synch with EM Repository Database
For Single Instance ,please do the following procedure:
1) Go to the database instance that you are not able to enter.
2) Choose Oracle Database ->Target setup ->monitoring Configuration
3) Enter all the information and make sure you enter the password correct .
4) Check the test connection
5) Save the Monitoring Configuration information
6) Give the saved monitoring configuration 5-10 minutes to process, access the target again
It should fix it....