How to proceed when encountering the message "An error occurred"?

When you modify a step in your campaign, you may see this error message when you save it:

This means that a script has been inserted into the source code of a text in the step. To remove it, simply click on the "Source" button.

And then delete the code added.

A script may be inserted into the source code of your campaign. This may be due to a browser extension you are using that automatically adds this script or to the duplication of a campaign created before Tag library was activated. However, once the Tag library has been activated in your account, it is no longer possible to add scripts directly to the source code of a campaign.

To use the Tag library correctly, please consult this FAQ.