I believe it is because of the fact that he's running powerlifting seminars. Probably falls under a sporting context, hence no IPF members should be in attendance. I don't know why people always use this stuff as an excuse to bash the IPF.
From WADA's own website:
"What is ‘prohibited association’?
There have been several high-profile examples where athletes have continued to work with coaches who
have been banned or with other individuals who have been criminally convicted for providing performance-
enhancing drugs.
A new feature of the Code taking effect at the start of 2015 makes it an anti-doping rule violation for you to
associate with this sort of “athlete support person” once you have been specifically warned not to engage
in that association.
THE DETAILS:
You must not work with coaches, trainers, doctors or others who are ineligible because of an anti-doping rule
violation or who have been criminally convicted or professionally disciplined in relation to doping.
Some examples of this type of prohibited association include obtaining training, strategy, nutrition or medical
advice, therapy, treatment or prescriptions. Moreover, the “athlete support person” may not serve as an agent or
representative. Prohibited association need not involve any form of compensation."