[imp] IMP can't connect mysql

[Man Chiu Lai]

Dear all,
I used horde 3, IMP 4, mysql 4.1.12, but when I connect mysql (e.g.
show tables in imp webpage) and always shows error messge "DB Error:
extension not found". I have attached the whole message in the below.
P.S. the login id and password is correct. If I type a wrong password,
the error message is can't connect. So the connection is already
established.

Also, in the left menu. It shows INBOX only by default. Can I change
to list all folder by default ?

Thank you very much!
Regards,
Gordon

error message
===================================================================
object(db_error)(8) {
 ["error_message_prefix"]=>
 string(0) ""
 ["mode"]=>
 int(1)
 ["level"]=>
 int(1024)
 ["code"]=>
 int(-25)
 ["message"]=>
 string(29) "DB Error: extension not found"
 ["userinfo"]=>
 string(41) " [DB Error: extension not found] ** Array"
 ["backtrace"]=>
 array(6) {
   [0]=>
   array(6) {
     ["file"]=>
     string(29) "/usr/local/php/lib/php/DB.php"
     ["line"]=>
     int(888)
     ["function"]=>
     string(10) "pear_error"
     ["class"]=>
     string(8) "db_error"
     ["type"]=>
     string(2) "->"
     ["args"]=>
     array(5) {
       [0]=>
       string(29) "DB Error: extension not found"
       [1]=>
       int(-25)
       [2]=>
       int(1)
       [3]=>
       int(1024)
       [4]=>
       string(32) " [DB Error: extension not found]"
     }
   }
   [1]=>
   array(6) {
     ["file"]=>
     string(31) "/usr/local/php/lib/php/PEAR.php"
     ["line"]=>
     int(540)
     ["function"]=>
     string(8) "db_error"
     ["class"]=>
     string(8) "db_error"
     ["type"]=>
     string(2) "->"
     ["args"]=>
     array(4) {
       [0]=>
       int(-25)
       [1]=>
       int(1)
       [2]=>
       int(1024)
       [3]=>
       string(32) " [DB Error: extension not found]"
     }
   }
   [2]=>
   array(6) {
     ["file"]=>
     string(36) "/usr/local/php/lib/php/DB/common.php"
     ["line"]=>
     int(1849)
     ["function"]=>
     string(10) "raiseerror"
     ["class"]=>
     string(4) "pear"
     ["type"]=>
     string(2) "::"
     ["args"]=>
     array(7) {
       [0]=>
       NULL
       [1]=>
       int(-25)
       [2]=>
       NULL
       [3]=>
       NULL
       [4]=>
       string(32) " [DB Error: extension not found]"
       [5]=>
       string(8) "DB_Error"
       [6]=>
       bool(true)
     }
   }
   [3]=>
   array(6) {
     ["file"]=>
     string(36) "/usr/local/php/lib/php/DB/mysqli.php"
     ["line"]=>
     int(281)
     ["function"]=>
     string(10) "raiseerror"
     ["class"]=>
     string(9) "db_mysqli"
     ["type"]=>
     string(2) "->"
     ["args"]=>
     array(1) {
       [0]=>
       int(-25)
     }
   }
   [4]=>
   array(6) {
     ["file"]=>
     string(29) "/usr/local/php/lib/php/DB.php"
     ["line"]=>
     int(556)
     ["function"]=>
     string(7) "connect"
     ["class"]=>
     string(9) "db_mysqli"
     ["type"]=>
     string(2) "->"
     ["args"]=>
     array(2) {
       [0]=>
       array(11) {
         ["phptype"]=>
         string(6) "mysqli"
         ["dbsyntax"]=>
         string(6) "mysqli"
         ["username"]=>
         string(5) "horde"
         ["password"]=>
         string(6) "lainet"
         ["protocol"]=>
         bool(false)
         ["hostspec"]=>
         string(9) "localhost"
         ["port"]=>
         bool(false)
         ["socket"]=>
         bool(false)
         ["database"]=>
         string(5) "horde"
         ["persistent"]=>
         bool(false)
         ["charset"]=>
         string(10) "iso-8859-1"
       }
       [1]=>
       bool(false)
     }
   }
   [5]=>
   array(6) {
     ["file"]=>
     string(47) "/usr/local/apache2/www/horde/admin/sqlshell.php"
     ["line"]=>
     int(32)
     ["function"]=>
     string(7) "connect"
     ["class"]=>
     string(2) "db"
     ["type"]=>
     string(2) "::"
     ["args"]=>
     array(1) {
       [0]=>
       array(7) {
         ["persistent"]=>
         bool(false)
         ["hostspec"]=>
         string(9) "localhost"
         ["username"]=>
         string(5) "horde"
         ["password"]=>
         string(6) "lainet"
         ["database"]=>
         string(5) "horde"
         ["charset"]=>
         string(10) "iso-8859-1"
         ["phptype"]=>
         string(6) "mysqli"
       }
     }
   }
 }
 ["callback"]=>
 NULL
}