sqlite3_prepare fails if SQLITE_OPEN_READONLY

sqlite3_prepare function fails if DB is opened with SQLITE_OPEN_READONLY.

Error message:  error #10: disk I/O error 
Sqlite extended error code: SQLITE_IOERR_LOCK (3850)
Errno: EBADF 9  /* Bad file number */

Everything works fine if DB is opened with SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE | SQLITE_OPEN_FULLMUTEX;

Any ideas on what may cause this problem?