Forms Authentication problems with virtual directory subdomain

[HippHopp]

the main website "domain.com" is a webforms 2.0 application with \[code\]Forms Authentication\[/code\] . \[code\] <authentication mode="Forms"> <forms loginUrl="~/LoginPage.aspx" protection="All"> </forms>\[/code\]now , I've added a subdomain by creating a virtual directory "/SubDomain" and converting it to application "subdomain.domain.com" . it's a \[code\]MVC 3.0\[/code\] application and uses \[code\]Forms Authentication\[/code\] too .\[code\]<authentication mode="Forms"> <forms cookieless="UseCookies" defaultUrl="~/home" enableCrossAppRedirects="false" path="/" requireSSL="false" loginUrl="~/account/login" protection="All" timeout="30" slidingExpiration="false" name="SubDomainAuthCookie"></forms></authentication>\[/code\]their membership system are independent using different databases .when I try to log into subdomain , I login successfully but :1- after moments it redirects me out of restricted area to login page . but I check the \[code\]cookies\[/code\] and "SubDomainAuthCookie" is still there !2- when it tries to redirect me to "account/login" the url is not correct . it is \[code\]subdomain.domain.com/subdomain/account/login?ReturnUrl=restrictedArea\[/code\]so can't find it.I searched but no success to find a solution . how should I fix this problem ?