Hello Zbynek,
I found the reason
The Yokogawa OPC Server is limited to 1000 item per group.
For me that means that when you use ReadMultipleItem there is only on group which is created in which all the items are put.
Is it right ?
How can I manage to avoid creation of only one group ?
Thanks you fro your answer

You are right
The exception raised is System.Runtime.InteropServices.COMException (0x80004005): ???????????
Do you have any idea ?
Thank you

Hello,
I have to read 3605 items which are separated as the 6 following Group

Group # 1 updateRate(s) 10 Count 740 Items
Group # 2 updateRate(s) 10 Count 766 Items
Group # 3 updateRate(s) 10 Count 374 Items
Group # 4 updateRate(s) 60 Count 790 Items
Group # 5 updateRate(s) 30 Count 763 Items
Group # 6 updateRate(s) 1 Count 172 Items

I used the function
daVtqResults = mDAClient.ReadMultipleItems(serverDescriptor, daItemDescriptors);
When I do this with the Group #1 I get 740 correct values.
When I do this with the Group #2 I get System.Runtime.InteropServices.COMException (0x80004005): in the Exception of daVtqResult
90% of the Group #2 are like this
The Group #3 is 100% with COmException
The Group #4 is 100% with COmException
The Group #5 is 100% with COmException
The Group #6 is 100% with COmException
When I read again Group #1 All the values are good
I created a small program which read a single value with easyDAClient.ReadItem
When I use it on one of the values which are given COMException the value is correct

So my question is :
Is there any limitation in DAClient concerning the multiple read ?
Thank you for your Help