Issue " The system is busy"

im facing an issue on WD My Cloud PR4100 at work with a message
" The system is busy. Please wait until the system LED turns solid blue before inserting another drive."
there are 2 hard drives 1 and 4 are lighting red led instead of blue led out of 4 drives, and all working in raid 5 !!! luckily data are ok
when i logged on thru its web page its was showing 2 hard drives bad status, the WD was running with no issue and our users they can see their files with no issue , i ordered 2 hard drives same specification as existing to replace them , after waiting for a couple of days i just wanted to replace the 2 faulty drives one by one, i took one out and replace with new one , then i go thru manual rebuild and then go thru its wizard , then it took about 5 mintuers then from the display says rebuild failed, then i mdae it auto rebuild then i did a restart, after restarting that message came up when i log on thru its page , and users now cant work with their files , its now 5 hours since this message appeared,
is that normal , please help me what to do

Still no updates , im just waiting for the warning message to go but still , now it completed 2 days with that message , im afraid of losing data , this most important,
i dont know shall i stop the process by taking the power off, then put the failed hard drive back to its drive 1 ??? or waht to do , or shall i wait but for how long
the good thing when i browes thru the ip address of the WD its showing the folders , so i hope it means the folders are there , but i cant access them
your suggestions is really appreciated