We are given a $0-1$ matrix $A$ with constant row and column sum, and we need to find out if there exists a $0-1$ vector in the solution space of $Ax = \mathbf{1}$ over $\mathbb{Q}$ (or $\mathbb{Z}$) where $\mathbf{1}$ is the all $1$ vector. If there exists such a binary vector then we would like to compute all of them or at least comment on the total number.

Are there any theoretical results in this direction? If not, then can we compute this without going through all $2^n$ possibilities where $n$ is number of columns of $A$?

In full generality it seems to be an NP-complete problem as pointed out here: http://mathoverflow.net/a/97140/34180. So, assume that $A$ is the incidence matrix of a highly symmetrical incidence structure (for example, a classical projective plane) whose full automorphism group is known.