My guess is incomplete reduction. Many of the aminoalcohols are solids with a mp above 80°C (D-norpseudoephedrine mp 77-78, +/- phenylpropanolamine mp 101-101,5). I also belive that a few of them can be pretty slow to dissolve in toluene. Phenylpropanolamine, however, should be easily soluble in toluene. But remember to saturate the aqueous phase with NaCl in order to push the amine out of solution. Many of them loves to hang out in water.
Reflux the solution for 30-60 minutes after all reactants has been added. This never hurts a reduction like this. Also, it can be a bitch to work blind. Check the reaction progress with TLC to, at least, see when the nitroalcohol is consumed.
My experience with reduction of nitro groups tells me that nothing can be taken for granted. Especially not when reducing aliphatic nitro groups. Some reductions works well with the theoretical, or close to theoretical, amounts of reducing agent. In other cases you need to hit the nitro compound with e.g. 8-10 mol Red-Al/mol nitro to get decent yields.
If you want to try the Zn/formate-system again use excess reactants and apply reflux for a while.