I guess you are trying to import an LSS file generated with LS 4.x into a LS 3.x installation? This is not possible, due to a change in the database structure in LS 4.x.
Help us to help you!
Provide your LS version and where it is installed (own server, uni/employer, SaaS hosting, etc.).
Always provide a LSS file (not LSQ or LSG).
Note: I answer at this forum in my spare time, I'm not a LimeSurvey GmbH employee.