[opencms-dev] Problem with Tomcat-Realms and OpenCMS 5.01

[Uwe König]

Hello *, 

I'm running OpenCMS 5.01 an encountered a problem. 
I want to grant access to a part of my VFS-folder structure only to
some users. My intention is that those users should not be able to
log into OpenCMS, so I created a Tomcat-Realm (MemoryRealm a.k.a
tomcat-users.xml) and added a SecurityConstraint to OpenCMS web.xml.

The nice thing is: this works fine the first time I
try to access a protected folder. Loginwindow pops up, and after
authenticating, I can see the page. 

Not so nice: if I'm closing my browser right afterwards, reopen
it and try to gain access again, after the login-popup I happen to
see not the intended page but: 

HTTP Status 503 - com.opencms.core.CmsException: 17 Service
unavailable. Detailed error: Cannot write output to HTTP response
stream. root cause was java.lang.IllegalStateException: getWriter()
has already been called for this response

Has anyone encountered this message also? Any hints for me? Has
anyone tried to combine OpenCMS with Realms / SecurityConstraints so
far? 
Many thanks in advance. 
Best regards, 

Uwe König