apache - htaccess rewrite stopped working after a while -

i have 2 sites:

site1.ru site2.ru 

it necessary implement such scheme, site1.ru/kv/ called site2.ru without url rewrite

i have used such structure

rewritecond %{request_uri} ^/kv  rewriterule ^(.*)$ http://site2.ru/login.aspx [l,p] 

but unknown reasons stopped working itself, , reason can not understand (the second server running on iis within local visibility)