Symptoms

Big files cannot be uploaded in File Download module through Sitebuilder Wizard. The following error is shown:

The file has not been uploaded. There is not enough disk space on the server where your site is hosted.

I have verified that publishing host does have enough disc space and permissions are correct. Smaller files are uploaded without any problem.
How to resolve the problem?

Resolution

Maximum size of uploaded file is limited in IIS.
Through configuration of Parallels Plesk Sitebuilder it is possible to overwrite the value.

It is recommended to enable and increase variables maxRequestLength and executionTimeout in file web.config on Sitebuilder server and publishing host.
Open file web.config and find directive httpRuntime:

  <!--
      <httpRuntime
        executionTimeout="190"
        maxRequestLength="4096"
      />
  -->

It is disabled by default.
Try uncommenting it and increase default values. For example:

  <!-- -->
      <httpRuntime
        executionTimeout="900"
        maxRequestLength="10960"
      />
  <!-- -->

File web.config is located in <Sitebuilder root>\Web\web.config on Parallels Plesk Sitebuilder server.
Where <Sitebuilder root> is Sitebuilder root directory. On publishing host the file is saved to site's publishing directory.

For example file location on Parallels Plesk Sitebuilder server:

C:\Program Files\SWSoft\Plesk\SiteBuilder\Web\web.config

File location on publishing host:

C:\Inetpub\vhosts\<site>\httpdocs\web.config