Taking a look at your expression from your notebook, it is of the general form:
a q^(? - 1) + b q^? == 1
This generally will not have a closed form solution for arbitrary
?. The error message (actually an informative warning message generateted by
Solve) is simply reflecting this fact.
(By the way, I am guessing that your e in your expression is meant to be the number
E in Mathematica. But that is irrelevant to your question as those factors are overall factors in your expression and don't affect the discussion.)
