Error: Cannot create unknown type, {}SendOutlookMail


Hi I had an interesting error here.

I used to publish the file correctly, and it worked well. But today I made little changes and published it again, it showed this error. However, it works good if I just run it on local PC and do not publish it.

I have double checked the activities folder, and project.json

Everything in the json file are in the activities folder, and mail activities are there, I didnt upgrade my uipath, only download some new packages recently, but they did not influence the mail activities at all.

I totally have no idea how to deal it, please help!


Buddy hope this would help you

As you say you were able to find all the activities available, I would like to suggest you one more thing update all the packages in UiPath studio, close the studio and open studio, now check buddy…



Hi Thanks

I have close & open the studio & restart my computer, it did not work.

I have checked this link before, that’s why I have ensure the things on the json are existing in the folder.

I have uninstall the mail activity and install it again, didnt work too.

Not sure if you know this but “Send Outlook Mail” requires the outlook application to be open and logged in (if using corporate account).

  1. So if this is running good in local PC, after your publish the nuget package; make sure the outlook application is open in VM and then run the job in that VM. See if that works.
  2. If that’s not a feasible option then use “Send SMTP mail” activity which doesn’t need you to open outlook for sending mails.

Let us know if that helps.

Hi Thanks for your advice

I know that outlook should be opened and logged in of course…
And my remote server one is also opened, it didnt work on my own PC’s ui robot, same error here.

I need to use outlook many times not only in this project, it is better can solve this rather than avoid it…

Hi All

I actually upgraded my office to 365 and upgrade my activities to the newest yesterday, is this relevant to this issue?

Because seriously I have published this one many many times before and used it for months and nothing wrong.

But for now, if i run it by studio, it works good. as long as I publish it, and try to run it by robot, it doesn’t work and pop up the error directly, so confused.

Solved, easy solution: uninstall uipath, reinstall uipath, works!

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