There is no for (neither it is possible to have) a comprehensive list of possible errors. You just need to look into the InnerException property of the exception, and you will find more details there.

You will probably find that the error message is "Value has bad quality". This errors occurs when you are using the ReadItemValue or ReadMultipleItemValues method, and there is real value returned by the OPC server - just a timestamp and an indication that the actual value cannot be obtained as is thus "bad". For the cause of the bad quality, one needs to investigate on the server side.

If you want to receive the full quality information (which sometimes contains a sub-quality that can tell you more) and a timestamp as well, you can use methods named ReadItem or ReadMultipleItems instead. They return the full VTQ (value/timestamp/quality) object, which you can then interpret yourself and make decisions in the code as needed. When everything else stays the same, however, using ReadItem instead of ReadItemValue in this situation will not give the error you reported, but you will still get a DAVtq object that will contain a bad quality indication, and no real data value.