Unable to login to Plesk: ERR [panel] Call to a member function getAttribute() on null

Symptoms

• The following error is shown when logging in to the Plesk:

ERROR: Call to a member function getAttribute() on a non-object (DefPackageMng.php:231)

Or

ERROR: Call to a member function getAttribute() on null (DefPackageMng.php:259)

• After logging into Plesk, white screen is displayed and the following errors are displayed in the browser console:
  

  PLESK_ERROR: TypeError: Cannot read properties of undefined (reading 'config')
  Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'config')
  Uncaught (in promise) Error: Cannot query field "webSocket" on type "Config".
  TypeError: Cannot read properties of null (reading 'select')
  Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'container')
  TypeError: Cannot read properties of undefined (reading 'logo')
  TypeError: E is undefined

• Repair Plesk installation options fails to work
• %plesk_dir%\admin\logs>php_error shows the following error:
  

  CONFIG_TEXT: [2023-07-05 04:40:17] 2452:64a4f43103ce2 ERR [panel] Call to a member function getAttribute() on null
  [2023-07-05 04:40:49] PHP Warning: DOMDocument::loadXML(): invalid character in attribute value in Entity, line: 2; File: C:\Program Files (x86)\Plesk\admin\plib\DefPackageMng.php, Line: 259
  [2023-07-05 04:40:49] 2452:64a4f451bf81e ERR [panel] PHP Warning: DOMDocument::loadXML(): invalid character in attribute value in Entity, line: 2; File: C:\Program Files (x86)\Plesk\admin\plib\DefPackageMng.php, Line: 259
  [2023-07-05 04:40:49] PHP Warning: DOMDocument::loadXML(): invalid character in attribute value in Entity, line: 2 in C:\Program Files (x86)\Plesk\admin\plib\DefPackageMng.php on line 259
  [2023-07-05 04:40:49] PHP Warning: DOMDocument::loadXML(): attributes construct error in Entity, line: 2; File: C:\Program Files (x86)\Plesk\admin\plib\DefPackageMng.php, Line: 259

Cause

The file %plesk_dir%\admin\db\defpackagemng.xml is absent or corrupted. 

Resolution

1. Connect to the server via RDP
2. Move the file %plesk_dir%\admin\db\defpackagemng.xmlto another location (if present).
3. Open CMD and run the command below to regenerate the defpackagemng.xml file:

   C:\> "%plesk_bin%\defpackagemng.exe" --get --force