Encountered Stack Trace in Category Hierarchies

I created a new category node but then deleted it due to wrong name and then created a new one. When I reopen the category hierarchy, only selected categories can be viewed. And when i select from the drop down list, I encountered a stack trace error. 

Also, in purchase requisition when I add items only the selected categories can be viewed (same with Category Hierarchy Setup)

See below:

Error executing code: object not initialized

Stack Trace

(C)\Classes\\data

(C)\Classes\EcoResCategoryTreeDatasource\expandAndSelect-line 60

(C)\Forms\EcoResCategory\Designs\DesignList\CategoryFindReferenceGroup\Methods\modified

(C)\Classes\FormRun\Wait

(C)\Classes\FormReferenceGroupControl\performFormLookup

(C)\Forms\EcoResCategory\Designs\DesignList\CategoryFindReferenceGroup\Methods\lookupReference

(C)\Classes\FormReferenceGroupControl\Lookup

(C)\Classes\FormStringControl\Lookup

What Steps should I do for this error.

Thank you for your help.