"This is about a very, very old software license that our client believed they had bought and paid for," he said. "It's our belief that our client's use of the software has been entirely consistent with the license they signed," he said.

Vaughan & Bushnell is happy with the software's performance and isn't interested in upgrading despite its advanced age, he added.

Assmus attributed Infor's move to the recession.

"I think any company, including Infor, is looking for additional streams of revenue," he said. "Contacting old customers about allegedly overdue fees is one way of doing that."