MK Dons striker Ryan Lowe, who played under Barker at Bury, was twice denied by the offside flag in the first half and again late on as the hosts failed to convert their dominance into a third straight win.
Lowe had a header and a tap-in ruled out early on before his close-range, half-volley was brilliantly saved by Paul Jones.
Dons forward Dean Bowditch also blasted a 25-yard drive inches wide of the post before crossing low for Daniel Powell to somehow blaze over the crossbar from four yards out.
The luckless Lowe dragged another good chance wide after the break and then had a third goal disallowed for offside after finishing well from a tight angle.
"It's a good point," said Barker. "I wasn't particularly happy with the first half, we worked on certain things that we weren't putting in place. So we talked again at half-time and we put them in place much better in the second half.
"We showed them a little bit too much respect in the first half but they're a very good side and they should be higher than where they are in the league.
"But to come here and keep a clean sheet and take away a point with some key players missing is excellent.
"I thought Lowe created too many problems for our centre-backs in the first half - I ended up selling him but he's very clever at what he does.
"Three goals disallowed for offside is good going and he put one over the bar from three yards as well. No doubt he'll ring me and moan about it later."