When a document is submitted to EC within an Annual Accounts previous version (for instance version 2017.0), the section to which the document belongs become 'not modifiable' in the next Accounts versions (2017.1, 2017.2, etc). Thus, the section name will be displayed in light grey.
In case you would like to submit other documents for this section, you will need to ask EC (through the Support Team) to set this section modifiable again.
Exceptions: the 'General>Document' section and the 'X-table data' section are always modifiable.