The Resolve Missing Files dialog shows when you have attempted to load a project file and some of the files were missing.

For each missing file, you will be prompted to either Delete or Resolve.
If you choose the Delete option for any missing file then that slide won't be loaded into the project.
If you choose the Resolve option then you will be prompted to browse to and choose a new file for that slide. Note that the new file must be of the same type as the original missing file.

Once you have resolved or deleted each missing file, click Finish to continue loading the project.

Media File Details

To open the Media File Details select the slide you want to view the details and then click on Slide -> File Details.... A dialog will show the creation time, the duration of the media and the current path to the selected file. Clicking on Change... will open a dialog that will allow you to select another file of the same type to use.

Missing Media Files

In the Media List the missing files will be shown with red text. To resolve these open the Media File Details, right click on the media you wish to resolve in the Media List and select Details....

You can locate the file by clicking the Change (Locate if file is missing) button and selecting the file path.