Please describe the url structure, do they all use the same host name like http://somwhost/mojo1, http://somehost/mojo2 etc or do theyeach have different host names?
If they all have the same host name it is likely a problem that they all use the same domain cookies so you may need to specify cookie paths according to their folders from Web.config.
So in the example above, I would try change the first site Web.config from this:
<authentication mode="Forms">
<forms name=".mojochangeme" protection="All" timeout="50000000" path="/" cookieless="UseCookies" />
</authentication>
to this:
<authentication mode="Forms">
<forms name=".mojochangeme" protection="All" timeout="50000000" path="/mojo1" cookieless="UseCookies" />
</authentication>
notice the Path changed to correspond to the folder the site runs in.
Hope it helps,
Joe