Getting error: "The located assembly's manifest definition does not match the assembly reference"

I'm setting up a Symantec Workflow 7.1.2 environment at the moment, but having an issue with one of our workflows that references the FirebirdSql.Data.FirebirdClient.dll. Version 2.0.0.0 gets initially installed with Symantec Workflow, but since my group knows that version of the dll is incompatible with this workflow, we've manually had to replace that dll with version 2.5.0.0 in our current workflow environments, where we see no issues.

So, in our newly set up environment, I'm running the workflow and getting the following error. However, only, when deployed. Running in debug results in intended behavior.

Could not load file or assembly 'FirebirdSql.Data.FirebirdClient, Version=2.0.0.0, Culture=neutral, PublicKeyToken=3750abcc3150b00c' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

System.IO.FileLoadException: Could not load file or assembly 'FirebirdSql.Data.FirebirdClient, Version=2.0.0.0, Culture=neutral, PublicKeyToken=3750abcc3150b00c' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040) File name: 'FirebirdSql.Data.FirebirdClient, Version=2.0.0.0, Culture=neutral, PublicKeyToken=3750abcc3150b00c' at CWx.Databases.Firebird.SqlQuery.GetAddressCheckHostname.Run(IData data) at LogicBase.Core.ExecutionEngine.SinglePathProcessComponentExecutionDelegate.Execute(IData data, IOrchestrationComponent comp, String& outputPath, IExecutionEngine engine, TLExecutionContext context) at LogicBase.Core.ExecutionEngine.AbstractExecutionEngine.RunComponent(TLExecutionContext context, IData data, IOrchestrationComponent comp)

What I've done so far is:

- Cleared out seemingly all traces of the workflow. The project folder, deploy folder, the IIS app pool and temporary .NET files. Restarted IIS and server.

- Reinstalled the workflow, manually added the new dll in the Libraries tab in Workflow Designer, checked the Publish checkbox.

- Validated that the old dll was replaced with the new one in both the install directory's \shared\lib folder and this specific workflow's \bin\ folder. I also added this dll into the server's GAC as an extra step.

- Added the following into the workflow's web.config file after deploying it:

<?xml version="1.0" encoding="utf-8"?>

<configuration>

  <system.web>

    <compilation defaultLanguage="c#" debug="false">

      <assemblies>

              <add assembly="FirebirdSql.Data.FirebirdClient, Version=2.5.0.0, Culture=neutral, PublicKeyToken=3750abcc3150b00c"/>

        </assemblies>

    </compilation>

...

I'm still getting the same error, but I have no idea where any references of the old 2.0.0.0 dll would exist. Anyone have any thoughts? Thanks.