When uploading files, you may get permissions errors. 

Sometimes DotNetNuke resets its file system permissions.

The reason that you are not able to upload files is because some specific security permissions need to be set.
1)  First, log in to your server and open up My Computer





2)  Select your C drive.





3)  Select Inetpub





4)  Select vhosts





5)  Select the domain that you're trying to upload in to.





6)  Right click on the httpdocs folder and click Properties.





7)  Select the security tab.  You will see three Plesk users.  Give each one Full Control and then Click Apply.  Next, click Advanced.





8)  Check the "Replace Permissions" box and select OK.





9)  Then click OK.