Elements AND Lightroom

If you use Photoshop Elements to organize and move your photos around, and they have already been imported into Lightroom, then Lightroom is going to lose track of them and tell you that they are missing.  The "normal" workflow is to use Lightroom to organize and perform initial adjustments, turning to Elements when necessary.  Most people will say that they are able to complete 95% of their work using Lightroom and turn to Photoshop or elements for occasional editing.