Now whenever I expand the Administrative Templates while editing an existing GPO, I get an below error message,
Encountered an error while parsing.
Expected one of the following possible elements(s), <test>, <decimalTestBox>, <testBox>, <checkBox>, <comboBox>, <dropdownList>, <listBox>, but found <multiTextBox> instead.
line 198, column 60
Above parsing issue is related to particular ADMX and ADML file, in my case it is related to four adml files. To solve issue simply remove admx/adml file from the PolicyDefinitions folder.
Take backup of the adml/admx files before removing it if you required.