The most common reasons for this error: 

1. The task is already completed in the CAT tool.
2. The source file is empty, or the code structure is broken. 

Offline work is needed in both cases. 

Download the source file and open it via Notepad++ or HTML Beautifier, depending on the file format, and proceed with the translation.  

Contact us via Translators-BLEND Talk or at support@team.getblend.com to receive further assistance completing the project.