Did you previously use another major version of SQLCipher? SQLCipher 4.0.0 introduces many new performance and security enhancements for applications that use SQLCipher for secure local data storage. However, the introduction of new default algorithms, increased KDF iterations and a larger page size means that SQLCipher 4 will not open older databases by default.
Please take a look at the documentation for upgrading to SQLCipher 4 here.