Make sure you have the Sitefintiy 3 site you are trying to migrate from and Sitefinity 5 site both hosted in IIS before trying to run the migration.
If you have used the automatic setup of the migration the project manager the project manager itself might not have permissions over your site folder to write the files for the migration to run so I recommend trying with the manual setup
of the migration. The manual setup is also described in the text file includes in the zip archive with the migration module assemblies.
the Telerik team
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