Greetings! I am new at working with Trados, learning. Can't edit any segment in the source document in Trados Online Editor. "Allow editing of source text in segments" is active. How could this problem be solved?

Greetings! I am new at working with Trados, learning. Can't edit any segment in the source document in Trados Online Editor. "Allow editing of source text in segments" is active. How could this problem be solved?