Cannot Upgrade or downgrade with webinterface

I cannot upgrade or downgrade my RB532A.
I upgrade to 3.0rc2 via ftp from another routerboard because I can’t upgrade from single package prom web interface.
I see that the file with web interface was uploaded to the rb but when the rb reboot..ther isn’t any upgrade..(or downgrade)
With the 3.0rc2 I’ve serious stability problems (rb crash every 2-4 hours) that I haven’t before.
Some wireless client connected to the AP con only ping the world (only packet size of 150byte ca) but any use of internet is impossible…
How I can force downgrade of my system?

At least on the 112s I’ve tried to work with the betas, I’ve never had the downgrade to function. Only sure thing was to netinstall the latest 2.9.