Hi Kerrie,

Does anyone else have access to the back-office?  I haven't seen this error before, but at a guess, I would think that someone (somehow) has removed the section/application access rights for your user.

If there are any other user accounts for the back-office, try logging in as them, see if the same error happens.

Which version of Umbraco are you using?

Thanks, Lee.

Hi Lee, thanks for your response

I've never seen this before either, just dont understand it.  There is just me which is the admin user and then I have two other users but they only have access to content and media sections so they couldnt have accessed any user accounts.

It is umbraco version 4.7.2

Hi Kerrie,

How comfortable are you with looking into the database? (If not, are you able to find someone who can?)

In your Umbraco database, take a look at the "umbracoUser2app" table data, see if your user account (if it's the root admin, then the ID should be zero) - make sure you have access to all the sections (e.g. "content", "media", "member", "settings", "developer" and "users")

Good luck!

Cheers, Lee.

Just checked the database and there I have access to content, developer, media, member, settings and users.  There shouldnt be any more listed on that table should there?

Yes, those are the correct ones.  Not sure what the problem might be, can the 2 other users log in okay?

They cant log in either.  I have downloaded the live database and tried running it on an older version of the website that I had on my local computer and that seems to work fine, but just not sure where the error could possibly be, there must be some difference in the files somewhere.

I have the same problem:

[ArgumentNullException: Value cannot be null. Parameter name: source] System.Linq.Enumerable.SingleOrDefault(IEnumerable`1 source, Func`2 predicate) +2715546 umbraco.BusinessLogic.User.GetApplications() +291 umbraco.cms.presentation._umbraco.Page_Load(Object sender, EventArgs e) +87 System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14 System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35 System.Web.UI.Control.OnLoad(EventArgs e) +91 umbraco.BasePages.BasePage.OnLoad(EventArgs e) +14 System.Web.UI.Control.LoadRecursive() +74 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2207

Does anyone have a solution?

If fix the problem in my site.

The problem was with the file "\config\ClientDependency.config"

I replaced it with original file "ClientDependency.config" and it worked.

The difference between the two files was that my file didn't had the tag "providers" instead there was some other tag.

There were other differences between the files but they were small differences.

Hope this helps those who encountered this problem.

I have the same problem, but my ClientDependency.config file looks just fine. 

I have tried to overwrite it too without any luck. Still no access to the backend.

Any other suggestions?

I couldnt get mine to work at all, in the end I ditched that version and went for the lastest version of Umbraco, no problems since.

My problem occured after a server crash...

The problem turned out to be the "applications.config" and "trees.config" was corrupted in the crash. After overwriting them with files from the backup everything was back to normal. *phew*

I also just had this same issue after a few files in an unrelated folder failed to FTP correct.y.  Both my /config/applications.cofig and /config/trees.config were corrupted.  Recopied these files and everything was back to nromal. 

Michael you rock!

I just had a crash too and this was exactly my problem. I thought I was going to have to nuke the whole db for a moment.

Thanks a lot Michael!

I too had the same problem and your solution saved my project.

What a bizarre issue.  Another +1 for Michael's solution.

Really weird.

Had zero-bytes applications.config and trees.config here too.

I started to get this same issue. Did you solve it? I cannot see the solution, or Michael's post for that matter... Am I missing something?

Hi Chris,

There seem to be posts falling off the forum all over the place (like Michael's).  I think the issue was that some of the config files had got corrupted.  Check trees.config and applications.config for starters.

Those two files were fine on mine - I ended up replacing the whole config folder as I didn't change any of the settings from the defaults.

Works okay for me now. Thanks for pointing in the right direction guys.

Weirdly though, I didn't have a server crash. I just checked with our networking team and can't find any errors at all on the server. Is there any other reason this type of error would occur?

I was the same issue.

I look that "Applications.config" and "Trees.config" was 0 byte length.
I solved replacing files with the right version.

The issue is generated by a "disk full" error in hosting server.

February 2016 and this still happens...most probably because of a "disk full" in the hosting server :)

Additionally, I can say that even though /config/applications.config and /config/trees.config were both with 1KB (or more), I've opened them with notepad++ and they were all full of "NULL" symbols.

Thanks Michael :)

This happens definitely because of disk full, It happened to many of my web sites and the disk was full.

When the disk is full this 2 files content is erased

• /config/applications.config
• /config/trees.config

To fix it just copy the original files from Umbraco vanilla (if you customize this file after copy costomize them again)

This will fix the problem !

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