It comes just four days after fellow recent arrival and Belgian compatriot Obbi Oulare was informed by the Home Office that his visa had finally been processed.
The continued delay in processing Iseka's paperwork provoked fierce criticism from Reds co-chairman Paul Conway, who lambasted the governmental department in no uncertain terms.
Speaking last Thursday, Conway said: "This is not acceptable. We send a player to Denmark and he gets a visa the same day...So both these players were approved to play in England and we are caught in the bureaucracy of the Home Office in not having a standard procedure for the issuing of these visas.
"Obbi was told by the Home Office to go to Belgium 18 days ago to get his visa. "Eighteen days and he just got it today (last Thursday).
"This is a joke, this is ludicrous. I don't understand this country, this is a big industry and we pay a lot of taxes here. "Why cannot we have a standard process for the timing of issuing of visas.
"The same thing with Aaron. He has been approved to play in England. So his deal was signed a week or so after Obbi so our logical assumption was that we'd get the visa in about a week.
"We have three sets of lawyers working on this and the Belgian Government actually helping out as these are Belgian citizens.
"This is a joke. At the same time, you see Manchester United and Chelsea get in players remarkably quickly and that is probably because they have better relations with the Home Office than Barnsley Football Club."
Both Oulare, who joined from Standard Liege and Iseka, a signing from French outfit Toulouse, are working on their fitness levels during the international break to boost their sharpness in preparation for the Reds' return to Championship action at Bournemouth on September 11.
Their availability would be a big boost with Carlton Morris sidelined for a spell with a knee injury.
Meanwhile, Barnsley are being strongly linked with a move for Wigan Athletic's former Leeds United left-back Tom Pearce, with the Reds in the market for a left-sided player ahead of Tuesday's transfer deadline.