Error after submitting form: To add an item to a document library, use SPFileCollection.Add()

Hi all,
I am a new user of plumsail, I would like to ask for advice where I can find information about this error:

To add an item to a document library, use SPFileCollection.Add()

It appears when I click submit after filling out the form I have prepared. I understand that it has to do with where the answer is saved?

Hey @DaveD,

Could you send the link to your form and a screenshot of the error message to
This way I can reproduce the issue and come up with a fix for you.

Hi Illia, I've sent it to support.

Hey @DaveD,

Seems like the problem might be that you are using an old version of Forms. You can check it on a form page in Sources, here’s how - Screen becomes white after a few seconds - #4 by mnikitina

Source files on the page must indicate webpart/

never mind, so I should update from to right?

Yes, you can find an instruction on how to do it in this thread: Lookup control doesn't work - #10 by IliaLazarevskii



also done, cleared all cookies, cache, site settings etc.
Saved again form plumsail form app

Unfortunately, same error :frowning:


Not what I expected at all.

Could you record a HAR log and send it to our support email?

Hi Illia,

Har log sent.

Hey @DaveD,

In Document Libraries, new forms are supported only for folder-derived content types, but it appears like you're trying to save a new form of a Document.

Could you describe your use case in more detail?
Maybe a default SharePoint new form would work better in this case?

@DaveD - I just completed this same update of webpart and widget via uploading a new App package. I am not saying that your experience is the same (my versions were quite a bit older than what you've shared), but curious if you're seeing other odd behaviors on your form? My JavaScript and CSS was impacted greatly after updating. Maybe you've figured out the problem already but can you comment out the offending block of JS and eliminate the error? I found that I had to rework my entire body of JS, to sort of reset the functionality. It was quite an effort and bet you're already beyond that point. Good luck.

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