Microsoft Security Essentials Update

Hello MSE, as an antivirus that updates through Windows Update, I think your problem is with Windows Update itself and not with MSE per se.
I advise you to check in the Windows help and support for issues related to updates.
Indeed, the error code you received comes from Windows Update.

Hello, if I may intrude into your discussion!
AmirBens the PC in question is indeed running XP, if so try to repair Windows Update with zeb-restore and if that doesn't work try with dial a fix. I’ll provide you with both procedures, and if nothing works we’ll need a diagnostic of your PC with ZHPDiag to see if we can find anything!

1) for zeb-restore

Download Zeb-Restore http://telechargement.zebulon.fr/zeb-restore.html and save this file on the desktop.

-Right click Zeb-Restore.zip ==> Extract all and choose the desktop as the save location.
-Open the folder ZR_1.0.0.37 ==> double click on Zeb-Restore.exe
-Check the boxes for: hosts file and then Windows Update
-Do not check any other boxes
-Click on Restore
-Restart your PC and see if you can update

2) for dial a fix

Download this program Dial-a-Fix

A "File Download" window will ask if you want to run or save the file,

click "Save".

In the new window, click on "Desktop" in the column on the left then "Save As" at the bottom right.

Once the program is downloaded, close your browser and right-click on the "Dial-a-fix" folder on your desktop.

Click on "Extract here" or "Extract all", a new folder "Dial-a-fix" will then be created.

Double-click on this "Dial-a-fix" folder and then on the file "Dial-a-fix.exe".

(You may get a window just before this indicating that problems have been detected.

Uncheck the "Hide disabled" box, then click "Remove" and "Close")

In the main window, click on "Check All" (the green button) to select everything.

Then click "GO" and let the software work.

Each ongoing action is highlighted and once completed it will automatically uncheck itself.

Finally, click on the "Flush SoftwareDistribution" button.

Once the repair is complete, close the Dial-a-fix window and restart the computer.

Finally relaunch Windows Update.

The updates should install correctly.

--
Personally, I may not know much, but if the little I know can help, then I'm happy to share it with you!!

Hello AmirBens,
Through which means do you call the MSE update?
Regards.

by the Microsoft Security Essentials window update tab

???
Error Code : 0x8024400A
Decimal error code translation : -2145107958
Error String : SUS_E_PT_SOAPCLIENT_PARSE
Description : failed in parsing response

And did you only have a communication error while downloading this update?
Have you tried again later?

Re,
If you're still in a bind, I suggest you try, one by one and in order, the solutions proposed by Microsoft here:
https://support.microsoft.com/fr-fr/help/836941
Best regards.

ADDENDUM

For the 0x8024400A errors encountered under MSE, there are nine topics in Microsoft social.answers! It's here: http://social.answers.microsoft.com/Search/fr-FR/?query=0x8024400A&rq=meta:Search.MSForums.ForumID%2846054a73-b5c5-4d8b-8da9-106b7ed5f8f4%29+site:microsoft.com&rn=Forum+Microsoft+Security+Essentials%3a+Updating+Virus+and+Spyware+Definitions

The superiority of IQ does not compensate for the mediocrity of the heart.

yes and I tried several times!

Il faut activer Windows Update pour que la mise à jour fonctionne correctement !

You need to enable Windows Update for the update to function properly!

I have tried all the solutions and I still can't get Windows Update to work.