ImportSolutionRequest for Default-Solution fails

Hi,

I implemented a Solutionhelper, which automates
export/import a solution. I exported the default-solution for backup purposes
(works fine). Now I want to import this solution on the CRM again. However, the
import fails with following error: EndpointNotFoundException (Error 404). I
also tried to import a custom-solution with success.

For me it looks like if there are some constraints for
default-solution-import.

Do you guys have any suggestions and maybe a
resolution for this problem.

Many thanks and best regards

Klemens

FileInfo importFile = new FileInfo(this.inPut);
if (importFile.Exists)
{
  ImportSolutionRequest impSolReq = new ImportSolutionRequest()
  {
    CustomizationFile = File.ReadAllBytes(importFile.FullName),
    PublishWorkflows = true,
                };
  this.service.Execute(impSolReq);
  this.PublishAll();
}//if