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RPC Server Unavailable in simple DA client

22 Dec 2020 07:11 #9308 by support

I do not have true explanation for this either. Internally, the software does do anything with the host name/address: It just passes it to underlying COM services. And as far as I can tell, both "localhost" and the actual IP address should work (provided that the "localhost" has its proper entry in the HOSTS file).


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21 Dec 2020 22:07 #9304 by janderscu
To answer your previous question .. this was a transient issue that threw the exception on the first data change event ... once the exception was thrown, no further data change events were triggered. I did not try other calls ... I only subscribe items this way. Thanks

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21 Dec 2020 22:04 #9303 by janderscu
Well, I figured it out ... trial and error. Turns out, I had to enter the actual IP of the machine I was working on when subscribing to the items ... instead of "localhost". I've never had to do that before with this client so it is something specific to the setup here. Not sure why. Any thoughts on where I might check for a DCOM or security setting somewhere that might affect this? Just in case we run into it again. THanks

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19 Dec 2020 11:14 #9299 by support
this exception is coming from DCOM infrastructure and is almost always related to setup problems or network errors.

I have some questions.

1. Are you saying that you *always* get this error in the DataChange event, being totally unable to receive the data, or is it just transient error?
2. Are other operations (such as Read, Browse) possible, or do they also return this error?
3. Is the server you are connecting to on the same machine, or remote?
4. When you refer to other OPC clients being able to subscribe, do you run them on the same client machine as were you have the problem?
5. Have you double-checked the machine name in the arguments passed to the subscribe calls?
6. Are you able to subscribe to some other servers (for example, if your desired server is remote on the network, can you subscribe to other servers on the network, and can you subscribe to local servers?)
7. What type of project is your application? (such as Windows Forms, WPF, Console app, Web app, Web service, etc.)?

Thank you

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17 Dec 2020 16:43 #9294 by janderscu
Hi, I am using QuickOPC 2020.2 Build 451.1 in a simple C# client that is subscribing to a DA server and monitoring data changes using the EasyDAItemChangedEventHandler. This client has been working fine on other machines and servers but running into an issue on a machine now where I get an exception in the DataChanged event with message: "RPC Server is unavailable" I know there are multiple sources for this error. I have turned off firewalls, etc based on reading I have done online on the subject. I do have other commercial clients I use for debugging that are not having this issue, they are able to find the server and subscribe to items fine. I can post code if needed. I appreciate any info to help debug this.

Thanks for the help.

Code to get exception:
static Exception GetException(EasyDAItemChangedEventArgs e_DA)
if (e_DA != null) return e_DA.Exception;
else return null;

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