There appears to be a bug in the dynamic category criteria page.  I have a number of dynamic categories, one of which displays new products.  I wanted to change the criteria for this today, so that it displays my 50 most expensive new items.  I changed the criteria to limit the number to 50 and left the product age to 30 days, and then changed the sort criteria to Price Descending.  The saving of the dynamic category settings went fine, but then the regeneration of the list returned an "Oops" red warning triangle error message.  It appears to be an error with the sort elements of the criteria selection.  If I leave the sort to it's default settings (Product Name, ASC) then it saves and generates fine.  If I set the sort criteria to anything other than the default settings, I get the error message on category regen.