Artifically limiting the number of items in a group is a serious OPC interoperability (and possibly OPC compliance) issue on the side of the OPC server, because a generic client has no way of knowing that such a limit exists and/or how big it is. Currently, QuickOPC does not have a feature that would "split" larger OPC groups into smaller ones.
You can, however, do the following: Create a separate EasyDAClient object for each "group" you want to work with, and set the EasyDAClient.ClientMode.Isolated property to True right after creating each of the EasyDAClient objects. This will cause these objects to use separate connection to the server (including OPCServer object, unfortunately, but that should not be a big issue), and therefore separate groups. Then, use ReadMultipleItems calls on these objects, limiting yourself to 1000 items or so, as you need.

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,
before we go further, I'd like to ask for this additional detail: During our phone call, you mentioned something like "access denied" error message. The error code below (0x80004005) actually corresponds to E_FAIL, i.e. "Unspecified error".
Can you please clarify this?
There are no hard-coded limitations to number of items, but some parameter tweaking may be needed for performance reasons in some cases. From the symptoms you are getting, it doesn't seem that this will be the case.
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