I just started to get this error using 4.4.0 with FTB when I open the Gallery:

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[] filenames, String[] cachekeys, CacheDependency dependency) at DotNetNuke.Services.Cache.FileBasedCachingProvider.FBCachingProvider.Insert(String CacheKey, Object objObject, CacheDependency objDependency, DateTime AbsoluteExpiration, TimeSpan SlidingExpiration, Boolean PersistAppRestart) at DotNetNuke.Common.Utilities.DataCache.SetCache(String CacheKey, Object objObject, CacheDependency objDependency, DateTime AbsoluteExpiration, TimeSpan SlidingExpiration, Boolean PersistAppRestart) at DotNetNuke.Framework.CachePageStatePersister.Save() at System.Web.UI.Page.SavePageStateToPersistenceMedium(Object state) at System.Web.UI.Page.SaveAllState() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---

Any clues?

I had the same error occurring from the modified store module - it turned out that on click of a link, the full file/pathnames of the skins & containers were being passed thru in the query string, thus making the URL too long.  I've seen this problem reported in quite a few modules - some people get a fix by modifying the settings as per previous post, but that turned out not to be the case for store.  Worth a try if you don't have any success with your settings.