Lots of questions that need answers.
What version of Premiere Elements are you using and on what computer operating system is it running?
Are you opening a new project or one that you already started and had saved/closed?
Is the message just "%s" or is the message "Where is file....?"
If applicable, is this the first time you are opening a project (old or new) in the Premiere Elements that you have?
Depending on your answers to the above, I may ask you for a screenshot of this "%s" message that you are
getting from the program. Do all projects that you open (old or new) give you the same message and does the
message prevent you from continuing in the project for import and export?
Looking forward to your follow up.
Welcome to the forum.
Along with the answers to ATR's very important questions, IF the message IS "Where is file ____ ?" where a file's name appears where I have typed underlines, then see this article: http://forums.adobe.com/message/4598705#4598705
Since Hunt has focused on my mention of the possible involvement of "Where is file ____?" messages in your problem, let me inject the following.
Often Replace Footage is preferred to use of "Where is file _____?" message for repair of the lost connection between the source media and the project. The key Replace Footage advantage is that the replacement retains the original edits. More on that later to determine which one of those options best applies to your specific situation if we are dealing with missing media..
My mention of "Where is file ____?" was to use the "Where is file _____?" message to identify the problem, not necessary use it to remedy the situation. But, your details will point us to whichever approach best serves your purposes. Both have perks to solve those very nasty reconnect issues.
We are getting ahead of the story without a lot more details from you.
Looking forward to those details from you.