Runtime Error
Method not found: 'System.String SD.LLBLGen.Pro.ORMSupportClasses.ConfigFileHelper.ReadConnectionStringFromConfig(System.String)'.
This is since upgrading to v5.5.3
Are you targeting .NET full or .NET Standard? Could you please make sure you are referencing the correct type of the SD.LLBLGen.Pro.ORMSupportClasses.dll ?
targetFramework="4.7.2"
I attached an image of the properties
Your post provided us insights on the proper dll to use.
The issue was resolved.