ORA-01033: ORACLE initialization or shutdown in progress

  Hi All,we are running 2 node rac 10gR2(10.2.0.4) on AIX6.1 and GPFS3.2 as cluster file system. today we have planed activity to bounce the instacne one by one so that user get unaware and stay working and its our routine paratice to bounce the RAC DB by instacnes one by One. every thing is fine we stop the instance one by below command 

srvctl stop instance -d dbname -i instance1

instance got stopped and then we initiate  

srvctl start instance -d dbname -i instance1 

 now when we execute the above command its completed successfully and come out on prompt. but for some time its starts giving subjective error and this situation stayed for 5 mints. and after 5 mints its got healthy. and during these five mints users that are using client side TAF servcie were getting subjective error.