The most common reasons for this message: 

• API issue.
• Server-side issue.
• Time-out due to inactivity.
• Bad internet connection.

To solve the issue from your end, check your internet connection, clear cache and cookies and try opening the workbench again. 

If the issue persists, please send us a screenshot along with the log details (data, time, browser) using support@team.getblend.com and we will assist asap.