[.NET] AmbiguousMatchException on initializing ServiceClient class

Hi guys.

I have an issue with initializing my service client created by AutoRest and inherited from ServiceClient.

It throws AmbiguousMatchException and it arises in ServiceClient class.

[AmbiguousMatchException: Multiple custom attributes of the same type found.]
   System.Attribute.GetCustomAttribute(Assembly element, Type attributeType, Boolean inherit) +122
   Microsoft.Rest.ServiceClient`1.get_FrameworkVersion() +103
   Microsoft.Rest.ServiceClient`1.SetDefaultUserAgentInfo() +177
   Microsoft.Rest.ServiceClient`1.SetUserAgent(String productName, String version) +50
   Microsoft.Rest.ServiceClient`1..ctor(DelegatingHandler[] handlers) +61

It only appears on my Remote machine with Windows Server 2008 R2 Standart .NET Framework 4.6.1. Locally on Windows 10 Anniversary 4.6.2 Framework everything is ok.

In Microsoft.Rest.ServiceClient I’ve found next part of code in ClientVersion property getter:

try
          {
            AssemblyInformationalVersionAttribute customAttribute1 = assembly.GetCustomAttribute(typeof (AssemblyInformationalVersionAttribute)) as AssemblyInformationalVersionAttribute;
            this._clientVersion = customAttribute1 != null ? customAttribute1.InformationalVersion : (string) null;
            if (string.IsNullOrEmpty(this._clientVersion))
            {
              AssemblyFileVersionAttribute customAttribute2 = assembly.GetCustomAttribute(typeof (AssemblyFileVersionAttribute)) as AssemblyFileVersionAttribute;
              this._clientVersion = customAttribute2 != null ? customAttribute2.Version : (string) null;
            }
          }
          catch (AmbiguousMatchException ex)
          {
          }

I think it is source of my problem but I don’t understand why it occurs and to handle it. I see that current exception must be caught but I don’t have any other ideas what else can be wrong.

Guys, any ideas ?

[shaunol]

Downgrading Microsoft.Rest.ClientRuntime from 2.3.3 to 2.3.2 has fixed the issue for me.

[robpex]

Adding info from my troubleshooting this problem.

In my case, the “Application Insights Monitor” (https://github.com/Azure/azure-content/blob/master/articles/application-insights/app-insights-monitor-performance-live-website-now.md) was injecting an additional “AssemblyFileVersionAttribute” value into mscorlib.dll. So, the Microsoft.Rest.ClientRuntime error makes sense because when it tries to get the file version using that attribute, it is, in fact, ambiguous.

1. Does it ever make sense to have more than one “AssemblyFileVersionAttribute” on any file? If not, there’s at least a bug in the tool I just mentioned.

2. Regardless of the answer to number 1, you’ll see that the code for Microsoft.Rest.ClientRuntime tries to use “AssemblyFileVersionAttribute” more than once. In one instance, it catches and ignores AmbiguousReferenceException and in other instances, it is not. I believe it should be consistent. Either it’s always safe to ignore it, or it’s not.