Verification Failed - Could Not Load File or Assembly

​​​Error Example:

Verification failed: Could not load file or assembly 'Microsoft.Exchange.WebServices, Version=15.0.0.0, Culture=neutral, PublicKeyToken=31bf3856sf364e35' or one of its dependencies. The system cannot find the file specified.

Verification failed: Error reading from entity 'CRM Online Users': Could not load type 'System.Data.Services.Client.DataServiceQueryContinuation`1' from assembly 'System.Data.Services.Client, Version=3.5.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'

Cause:

When errors like this appear during connection string validation, it usually is due to an installation problem with the provider itself and it cannot find the file information for the provider.

It can also show up when two versions of the Cloud Connector application are installed, or if a prior Cloud Connector or BDLC install was not cleared out of the assembly cache correctly, leading to assembly conflicts.

Specifically, regarding the Exchange provider - it requires that .NET 3.5 Framework be installed, even if the core machine is .NET 4+, else it will throw this error.

Resolution/Workaround:

Check if the missing assembly is covered by one of the specific resolutions below. If not then please see the General Resolution section.

Microsoft.Exchange.WebServices

This applies to the Exchange provider - an error will appear that this is missing​ when you try to validate an Exchange connection. You must uninstall the Cloud Connector, enable/install the .NET Framework 3.5, and then reinstall the Cloud Connector to clear this error. Helpful links for the user:

Enable .NET Framework 3.5 by using the Add Roles and Features Wizard

Download Microsoft .NET Framework 3.5​

Layer2.License.Interfaces

This applies to having multiple copies of the Cloud Connector installed, or maybe due to collision with older assemblies that were not properly uninstalled. More commonly seen with version 7.8+.

First, you should perform a 'Clean Install' - You should remove any and all copies of the Cloud Connector in the Programs and Features list, as well as the Layer2 ADO.NET providers from BDLC, if that was also installed at some point.

If the issue persists you should check the Cloud Connector installation folder (usually here: C:\Program Files (x86)\Layer2 Cloud Connector), to verify the assembly is present. If not, then there still was an installation error and you should uninstall/reinstall. Then you should check the Global Assembly Cache (usually here: C:\Windows\assembly), and remove any Layer2 assemblies listed (usually will be the one in the error message that will be present).

 

Layer2.SharePoint.Resources​

This has been observed after Windows updates. In most cases, a repair-install solved the issue.

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System.Data.Services.Client

In this case, the .NET Framework is probably not up to date. You should be able to patch and update the Windows OS and .NET Framework to clear this.

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General Resolution

Uninstall all currently installed versions of the app via the Programs and Feature page. Reinstall the newest version.