Sage.Reporting.Engine.Integration - "invalid report file" error when trying to run report

We are using Sage Accounts 50 v28. I am trying to write sample report generation app using C# and I am stuck at very beginning because Sage is reporting me back that report file which I am trying to use is not valid even if it runs without any problem when I am running it directly within Report Designer. I have managed to get longer backtrace of the error so if anyone can help me with that or provide some developer resources / documentation it will be great.

Exception has been thrown by the target of an invocation.
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Span`1& arguments, Signature sig, Boolean constructor, Boolean wrapExceptions)
   at System.Reflection.RuntimeMethodInfo.InvokeOneParameter(Object obj, BindingFlags invokeAttr, Binder binder, Object parameter, CultureInfo culture)
   at System.Reflection.RuntimePropertyInfo.SetValue(Object obj, Object value, BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo culture)
   at System.Reflection.RuntimePropertyInfo.SetValue(Object obj, Object value, Object[] index)
   at Sage.Xml.Serialization.XmlSerializer.LoadProperty(Object obj, Type type, XmlReader reader)
   at Sage.Xml.Serialization.XmlSerializer.LoadProperties(Object obj, Type type, XmlReader reader)
   at Sage.Xml.Serialization.XmlSerializer.Load(Object owner, XmlReader reader)
   at Sage.Xml.Serialization.XmlSerializer.LoadXml(XmlReader reader)
   at Sage.Xml.Serialization.StreamSerializer.LoadFromStream(Stream stream)
   at Sage.Reporting.Engine.Model.ReportFile.LoadStream(Stream stream, Boolean cloning, String[]& unrecognizedTypes)
   at Sage.Reporting.Engine.Model.ReportFile.LoadFile(IReportFile reportFile, String[]& unrecognizedTypes)
   at Sage.Reporting.Engine.Model.ReportFile.LoadFile(IReportFile reportFile)
   at Sage.Reporting.Engine.Integration.ExportService.ExportBatchItem..ctor(ExportService parentService, String filename)
   at Sage.Reporting.Engine.Integration.ExportService.Sage.Reporting.Engine.Integration.IExportService.Load(String filename)