You have some switched commas and quotes right here:
concat("SetValue /xpath=dfs:myFields/dfs:dataFields/tns:GetFormDatasetResponse/tns:GetFormDatasetResult/ns1:dsForms/ns1:Clients[, "
That should be [",
That being said, it seems like it might be helpful to clarify for you how the concat formula works. The concat formula takes as arguments comma separated values, like:
concat(field1, field2, "Some text")
Anything that is a field or a formula would not be in quotes, anything that is a regular bit of text would be in quotes, like the concat above. So, let's pretend that field1 has a value of "grape" and field2 has a value of "orange" and we are going to display our concat formula in an expression box on our form. We'd see this in our expression box:
grapeorangeSome text
Not too pretty. We can modify our formula to include some spaces!
concat(field1, " ", field2, " Some text")
Now we'd have
grape orange Some text
Mind you, the text makes no sense, but at least it is nicely formatted. For more about basic formulas and functions in InfoPath, check out this Office Online article. And this one, and this one, too.