Since no one has replied to your question, I will try to hep you. Fist of all, I have never used Algor, but have done a lot of FEA over the years. As Adolph Hitler was fond of saying, (in German of course) "there are two possibilities" :

1. You have underconstrained your model
2. There is something wrong with the software

The second possibility is unlikely, but possible.

Exactly how did you constrain your model ? It must be fixed to ground so that at least all six bodily displacement degrees of freedom are constrained (three translations and three rotations). One implication of this is that, with plate elements, if you are fixing just one edge, you must in many cases constrain at least some of the rotations at the edge nodes as well as the displacements. Maybe you neglected to do this. You shouldn't need to constrain the rotations in the plane of the plates. This assumes that your version of Algor has automatic removal of uncoupled (and unused)degrees of freedom - most modern codes do - but this is where my lack of specific Algor experience is a problem.
Maybe you have figured it out by now - but good luck anyway.

I just spent 2 days working with this exact problem.

We had our model fully constrained, but our geometry was not correct.  Algor does not like elements runing into other elements where there is not an endpoint.
Try constraining first, but if it does not work.
Start looking to change a few lines here and there to make them more ALgor friendly.