how to read more data in a packet by CIP read data service(4C)

hello all:
I want to read more data in a tcp packet using 4C(open connection).According to the AB logix data access manual:

the read data service :The CIP read data service reads a block of data starting from the specified address at the IOI string:
Command format
Service code(4C) -- IOI string --size
If I want to read five data starting from 'a',I set the size for 5 and send the following packet to PLC,but response wrong message,anyone can help me ,thanks a lot.


Service: Open Connection (Request)
0... .... = Request/Response: Request (0x00)
.100 1100 = Service: Open Connection (0x4c)
Request Path Size: 2 (words)
Request Path: a
Extended Symbol Segment (0x91)
Data Size: 1
Data: a
Pad Byte (0x00)
Command Specific Data
Data: 0500

the response :

Common Industrial Protocol
Service: Open Connection (Response)
1... .... = Request/Response: Response (0x01)
.100 1100 = Service: Open Connection (0x4c)
Status: Unknown Response (ff), Extended: 0x2105
General Status: Unknown (0xff)
Additional Status Size: 1 (word)
Additional Status: 0x2105