I've never had this problem before with Elements 9, but I attempt to get media from files, select 46 Mp4 Video Clips and it will only import 36 of them. I've rebooted the computer,that doesn't help. I cannot select the project from the filter drop down most of the time, although I can see it. I have to use another method. Even when it works, there are only 36 out of the 46 videos there. I attempt to import the other 10 manually... it acts like it does as you see the progress bar but they are not viewable. I finally was able to accomplish this after having to manually count the videos since there is no indicator, by accessing the Large Project Icon under Organize, but it's not the way I'm used to draging my video clips down to the timeline. Not sure what is wrong and why it has developed this new behavior. Had I not been manually counting them (odd that there is no number of files indicator) I would have completed a project and would have been missing 10 video clips.
Please perform the following computer maintenance...
a. Adobe Folder. Look for pile ups in the Adobe Premiere Elements Preview Files Folder and delete them. Look for pile ups in the Media Cache Folder (conformed audio cfa and pek files) and delete them.
b. Edit Menu/Preferences/Media. In the Media Cache section, click on the Clean button to get rid of the conformed video (.mcdb) files.
c. Run the ccleaner, regular cleaner and registry cleaner.
As far as you can determine how do the 10 differ from the 46 videos. What is the hard drive save location for these 46 videos and is that drive formatted NTFS or FAT32? The properties of those videos (aside from the .mp4 file extension) would be included in your exchange of information, along with project preset.
Since you are working with a 32 bit application in Premiere Elements 9.0/9.0.1 with all the limitations of a 32 bit system, I am thinking that the issue probably goes to level of computer resources and maintenance.
Let us see if we can sort this out. There are other avenues to pursue but the above seems more indicated at this time.