where can I retrieve the version of Router OS v5.0rc10 or v5.0rc9?
Thanks
why do you need an older version, and for what architecture
I do a downgrade because the v5.0rc11 is very unstable part radio ra
disconnects all the time I need to Rb411AH and for the RB800
Thanks
have you contacted support with a supout to support@mikrotik.com? i know they are handing out rc12 for some problems, otherwise http://www.mikrotik.com/download/routeros-ALL-5.0rc10.torrent
I recommend following jtroybailey’s advice and generate a supout.rif and email it to support(at)mikrotik.com with a short explanation of the problem.
I personally would like to see your log entries from one of the disconnects on both the AP and the station. If you can, enable verbose wireless logging.
/system logging
add topics=wireless,debug action=memory
Here is a thread that covers a lot of the disconnect problems, along with the advice from uldis to send a supout and get rc12. That post is down near the end.
http://forum.mikrotik.com/t/log-reassociating-disconnected-ok-connected/44784/1
Please let them know if that fix worked or not. And us too! 
hy jtroybailey
how do I migrate from the 5rc11 to 5rc10?
upload the routeros npk file appropriate for your hardware to the root folder of the system (either via drag and drop into files) or via ftp and then, if using winbox, go to system, packages, then click on downgrade.
Check if you need any other packages which are not included in the “all in one” single file you’ve uploaded and upload them as well, such as the ntp server package before downgrading.
where can I retrieve the version 5.0rc12?
contact Mikrotik Support. It’s not available publicly yet.
write to support@mikrotik.com and we can give you a test version of RouterOS v5.0rc12