Hello Ricard Bertran Vall,
cannot select multiple files in one file select box. This is a limitation of the standard <input type=file>
elements that RadUpload
uses for file selection. Currently, there are no plans for changing this restriction. You can check this code-library: How to upload multiple files using RadUpload (uploading .zip file and extract it on the server)
Alternatively, you can use RadUpload for Silverlight. See this demo
for further details.
the Telerik team