We have been getting a lot of these exceptions lately. I looked at our source code, and it seems to be related to the amount of locks returned by the servlet, although very inexplicit.
Have you seen these from other customers, and do you know the cause? We use office-connector v.1.18
ERROR 31 Oct 2012 08:44:16,080 tomcat-5 com.atlassian.confluence.extra.webdav.servlet.ConfluenceWebdavServlet Unexpected error
Oct 31 08:44:16 10.126.15.221 org.apache.jackrabbit.webdav.DavException: Precondition Failed
Oct 31 08:44:16 10.126.15.221 at org.apache.jackrabbit.webdav.server.AbstractWebdavServlet.doLock(AbstractWebdavServlet.java:682)
Oct 31 08:44:16 10.126.15.221 at org.apache.jackrabbit.webdav.server.AbstractWebdavServlet.execute(AbstractWebdavServlet.java:258)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.confluence.extra.webdav.servlet.ConfluenceWebdavServlet.service(ConfluenceWebdavServlet.java:104)
Oct 31 08:44:16 10.126.15.221 at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.DelegatingPluginServlet.service(DelegatingPluginServlet.java:42)
Oct 31 08:44:16 10.126.15.221 at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.ServletModuleContainerServlet.service(ServletModuleContainerServlet.java:52)
Oct 31 08:44:16 10.126.15.221 at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
Oct 31 08:44:16 10.126.15.221 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
Oct 31 08:44:16 10.126.15.221 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:46)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter$1.doFilter(DelegatingPluginFilter.java:66)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.confluence.extra.webdav.servlet.filter.ReverseProxyCopyAndMoveDestinationFix.doFilter(ReverseProxyCopyAndMoveDestinationFix.java:59)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.confluence.extra.webdav.servlet.filter.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:34)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:74)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:42)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter$1.doFilter(DelegatingPluginFilter.java:66)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.confluence.extra.webdav.servlet.filter.MicrosoftMiniRedirectorAuthenticationHeaderFix.doFilter(MicrosoftMiniRedirectorAuthenticationHeaderFix.java:72)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.confluence.extra.webdav.servlet.filter.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:34)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:74)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:42)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter$1.doFilter(DelegatingPluginFilter.java:66)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.confluence.extra.webdav.servlet.filter.ClientWriteDenyFilter.doFilter(ClientWriteDenyFilter.java:43)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.confluence.extra.webdav.servlet.filter.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:34)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:74)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:42)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter$1.doFilter(DelegatingPluginFilter.java:66)
Oct 31 08:44:16 10.126.15.221 at com.bloomberg.confluence.plugin.OrgchartFilter.doFilter(OrgchartFilter.java:55)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:74)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:42)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:77)
Oct 31 08:44:16 10.126.15.221 at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:63)
Oct 31 08:44:16 10.126.15.221 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
Oct 31 08:44:16 10.126.15.221 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)