AI Center Error while importing PDF documents to Data Label

In AIC, I am using UiPath Document Understanding. I want to data label my PDF documents and create ML Skill which I can use in my DU BOT in studio. While doing this, I am struck at the first step of data manager.

When I click on import PDF documents, The import status is showing below error on all documents that I have selected. please help me resolve it

7/15 [PROCESSING]: Sample_PDF.pdf
[FAILED]: Sample_PDF.pdf Failed to process document Sample_PDF.pdf: Error receiving response