The current questionnaire is not valid, therefore it cannot be changed

Hello everybody,

I am trying to make some minor changes to a Survey:

I select a Question,

then right clik and choose "Insert Answer"

Answer Category, select "4 Input Field for Date"

then I write the Text: "Field X" in the Answer option (Field X for example)

Please note that I have working Field Y, Field Z, etc, with the same attributes, in the same Survey

Then I save , and activate the new version of this Survey,

but when I test in Web client, it shows the SAP message "The current questionnaire is not valid, therefore it cannot be changed"

then in SAP GUI the Survey automatically generates a new version of the Survey, with my changes erased  (back to original Survey).

Any ideas are appreciated, Thank you.