Execution Error: Execution error : System.Xaml.XamlObjectWriterException: Cannot create unknown type '{http://schemas.uipath.com/workflow/activities}SendMail'

[Adit2917 (Adit Sunil Kansara)]

We have developed a workflow and have been testing successfully in the development environment for over a month. After successful execution in the development environment, we moved the package to the prodroduction environment. But I don’t know why out of nowhere this error popped up. Is there anything we need to do to set up for production environment? This is an unattended bot, so we don’t have studio setup in prod envt.

[Dominic]

Cannot create unknown type error comes when the activity that is mentioned after the schema URL (https://schemas.uipath…) i.e SendMail (that is part of UiPath.Mail.Activities) is not available

From the error message, seems that the robot machine doesn’t have the exact version of the UiPath.Mail.Activities which is added as a dependency for that project.

Steps to resolve:

1. Open project.json of the project & verify the UiPath.Mail.Activities version
2. Please check if the robot machine has the same version of that package in %userprofile%.nuget\packages (if the robot version is >= 2018.2) or %localappdata%\uipath\activties (if the robot version is < 2018.2) or your customized package installed path location (if the robot version is >= 2018.4.4)
3. If the above directory doesn’t contain the version, to resolve temporarily copy the exact version of the UiPath.Mail.Activities.{versionNumber}.nupkg from a working environment\machine and place it in <Installation directory of UiPath Robot>\packages folder
4. Long term solution is to whitelist the online feed (myget.org & nuget.org, *.vo.msecnd.net) where the packages are automatically downloaded from the below feed as shown:
   

Detailed explanation: Cannot create unknown type - V2018.2.3 Onwards - Troubleshooting steps