Check On the Primary database and the following status will appear to you :
SQL> select name ,open_mode, database_role, switchover_status from v$database;
NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STATUS
MAN MOUNTED PHYSICAL STANDBY NOT ALLOWED
To make sure everything is Ok on both Side Primary and Standby :
SQL> select name ,open_mode, database_role, switchover_status from v$database;
NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STATUS
MAN READ WRITE PRIMARY TO STANDBY
Another Check :
On Primary Database :
SQL> select max(sequence#) from v$archived_log;
MAX(SEQUENCE#)
56
At Standby :
SQL> select max(sequence#) from v$log_history;MAX(SEQUENCE#)
56
You Solve this problem By Fire the below command :
SQL > alter database commit to switchover to physical standby with session shutdown
The Above Command Should be Run on Primary Database to Generate Special marker on Online Redolog Headers Which Mean transfer the archive to standby , after that the status should be changed.
Please check the below Link from OTN Forum that describe the same problem also and The Solution is Mentioned already there:
1- Not allowed status in primary db switch_over status Press here.
2- Not allowed Issue while DR switchover Press here.
Thank you
Osama Mustafa
Technology Geek 