Please accept our apologies for the inconvenience caused.
This issue is already fixed and it will be released with the Service pack for Q1 release, currently planned for the end of April.
The exception was thrown when you regenerate your RLINQ file which with the last version of OpenAccess ORM is generating the ISofiaCarRentalEntityDiagramsUnitOfWork interface in the model file (the SofiaCarRental.cs one) but the sample was made when this interface was not created automatically.
In order to fix this issue you can delete the old UnitOfWork.cs file from the SofiaCarRentalDAL project (the one which is selected in the attached image).
Please bear in mind that in order to fix this issue permanently (even if you reset the sample), you will need not only to delete the file from the samples cache folder of the Samples Kit (the one which is opening when you click Open Sample Folder) but to delete it from the samples folder in the OpenAccess installation folder too (you could find the file at OpenAccessInstallDirectory\ProductSdk\Content\Samples\
I hope this is applicable for you.
the Telerik team
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