WebDAV request returns 500 Internal Server Error

amohdaris@amohdaris-Precision-T1500:~$ cadaver https://zebrathings.atlassian.net/webdav
Authentication required for Studio WebDAV on server `zebrathings.atlassian.net':
Username: sysadmin
Password: 
Could not open collection:
500 Internal Server Error

[Mon May 28 10:27:38 2012] [error] [client 123.456.789.10] Application failed to authenticate as 'webdav' to Crowd at 'http://localhost/crowd/rest/usermanagement/1/authentication?username=sysadmin'.
[Mon May 28 10:27:38 2012] [crit] [client 123.456.789.10] Crowd authentication failed due to system exception

2012-05-28 10:33:30,935 TP-Processor16 INFO [plugin.rest.filter.BasicApplicationAuthenticationFilter] Application 'webdav' failed authentication