Here is the log entry for it:
ExceptionGUID: 66d9ef2b-4a7e-4748-a4ba-250a075582aa
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
InnerException: The specified path, file name, or both are too long. The fully qualified file name must be less than 260 characters, and the directory name must be less than 248 characters.
Message: DotNetNuke.Services.Exceptions.PageLoadException: The specified path, file name, or both are too long. The fully qualified file name must be less than 260 characters, and the directory name must be less than 248 characters. ---> System.IO.PathTooLongException: The specified path, file name, or both are too long. The fully qualified file name must be less than 260 characters, and the directory name must be less than 248 characters. at System.IO.Path.NormalizePathFast(String path, Boolean fullCheck) at System.IO.Path.GetFullPathInternal(String path) at System.Security.Util.StringExpressionSet.CanonicalizePath(String path, Boolean needFullPath) at System.Security.Util.StringExpressionSet.CreateListFromExpressions(String[] str, Boolean needFullPath) at System.Security.Permissions.FileIOPermission.AddPathList(FileIOPermissionAccess access, AccessControlActions control, String[] pathListOrig, Boolean checkForDuplicates, Boolean needFullPath, Boolean copyPathList) at System.Web.InternalSecurityPermissions.PathDiscovery(String path) at System.Web.Caching.CacheDependency.Init(Boolean isPublic, String[] filenamesArg, String[] cachekeysArg, CacheDependency dependency, DateTime utcStart) at System.Web.Caching.CacheDependency..ctor(String filename, DateTime start) at System.Web.Caching.CacheDependency..ctor(String filename) at DotNetNuke.Services.Cache.FileBasedCachingProvider.FBCachingProvider.Insert(String CacheKey, Object objObject, Boolean PersistAppRestart) at DotNetNuke.Common.Utilities.DataCache.SetCache(String CacheKey, Object objObject) at DotNetNuke.Modules.Forum.DNNForum.get_Menu() at DotNetNuke.Modules.Forum.Groups.CreateChildControls() at DotNetNuke.Modules.Forum.DNNForum.CreateChildControls() at System.Web.UI.Control.EnsureChildControls() at DotNetNuke.Modules.Forum.ForumBaseControl.EnsureChildControls() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---