HI Anca,
Once I add the webpart in Master page, the tagprefix is also automatically registered.
Based on your answer on top, I had an impression, we need to add it specifically after adding the webpart.
I am fine now and thanks for your reply.
An observation I noticed which might be useful.
If we try to change the webpart properties either by Design or Code after added and saved the master page with webpart, SharePoint throws Coorelation id error.
Once we delete and re-add the same webpart with all required properties, it works fine.
So just remember, for first time when you add the webpart, Set all the properies that are required. Period.
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