Premiere Elements 2020 not recognizing prel files that it created

[MamaBebe]

I have created files in Premiere Elements 2020, which have been saved as .prel files. Often when I attempt to open these files in Premiere to continue editing, I get this message: 

This type of file is not supported, or the required codec is not installed.

Most of the time I cannot open prel files at all. Sometimes a prel file will randomly open, but some clips are 'offline' and are just a red cryptic field saying offline.

[Steve Grisetti]

What are the steps you are using to open the .prel files? It sounds like you may be using Add Media to open a project file, which will not work.

To open a .prel project file, you must use File/Open.

[Bill Sprague]

Not much to go on here, but my guess is that the source files are not where they were when the project was last opened.  

When you say that you can't open .prel files, how and with what are you opening them?