Duplicate field within hidden system content type

[Yaron Ben Shalom]

We have a SP 2013 project with some content types.

We have been updating this project for several years with no problem.

Lately we have encountered an issue where new updates cannot be deployed because one of our fields has a duplicate within a hidden, system content type (System Media Collection).

We are unable to remove the field from that content type since the FieldLinks collection is empty within said content type and attempting to delete the field directly results in an

"Exception calling "Delete" with "0" argument(s): "This functionality is unavailable for field collections not associated with a list."

Any ideas?

[#2]

Hi @Yaron Ben Shalom, did you already think about to migrate your concerned data to MODERN SharePoint Sites? Two main reasons i can imagine: 1) a "duplicated field" within 2 content types sounds crazy and if ever possible SharePoint likes only unique column names. I guess, there are certain site columns, and you should try to first delete the already empty and error causing site column - if this site column is empty and not linked with any content in several sites. If this site column is deleted, and the next step you can delete the content type. Every linked data in a site column within a content type causes your described error, i guess.

2) In SharePoint online and modern SP Sites i already have all content types and site columns within my SharePoint Admin Center. If you only are a Site Owner and no Site Admin, maybe you don´t have permission to change content types and maybe your SharePoint is now in transition from classic 2013 sites to modern Sites? I can only guess. The link error can be in the hidden part of your root site, maybe in a lookup (site) column and there is the relationship option within this special column. Did you already deactivate this relationship option (check box) within the site column settings? If you are able to look into the site column settings, you can deactivate this field link and then you can possibly delete that double trouble column... But before deleting make sure that there isn´t any related data in this list!! No disclaimer on my side. 

Hope that helps a bit, greets, Eva.

[#3]

@Eva Vogel This is SP 2013 so no modern sites/pages.

Right now I don't think the fact that the site column found its way into the system CT but rather that SP is convinced there is a duplicate field while we cannot find any, either by name or ID.

BTW, the field name in question is "CatalogNumber".

[#4]

Hello @Yaron Ben Shalom, di you also check the managed metadata? In searching for the key words "SharePoint CatalogNumber" the results tend to look into crawled metadata and their links to site columns. Maybe these links are causing this? I am not so familiar with the managed metadata stuff. A very good source on that topic is https://www.youtube.com/watch?v=tjvb5VV4lVE , a video about advanced Search, KQL from Joelle Jobson and Laura Rogers (iwmentor.com), maybe that helps. Greets, Eva.

[#5]

@Eva Vogel I don't see any connection between Managed metadata and the issue we have here, to be honest.

We may try to split the feature so the updates we require (that have nothing to do with the presumably duplicate site column) are made independently.