Unable to insert new page.

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Hi
When I try to insert another page I get this. I've tried upgrading and now on 8.4.5.

An exception occurred while executing 'insert into Pages (cID, siteTreeID, ptID, cParentID, uID, cInheritPermissionsFrom, cOverrideTemplatePermissions, cInheritPermissionsFromCID, cDisplayOrder, pkgID, cIsActive, cIsDraft) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)' with params ["420", null, "6", null, "1", "TEMPLATE", null, 153, 0, 0, 0, 1]: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'cParentID' cannot be null

Can anyone help please ?
Many thanks

tjbphoto