When did he ask Anakin not to come along? He may be assigned to another task by the Jedi Council and couldn't help Obi.
In the novel Shadow Conspiracy.
"And the Jedi Council will do nothing, of course." Anakin said disgustedly.
"It's not as simple as that," Obi Wan said reluctantly. "The Senate_"
"The Senate will do even less," Anakin said. "But we're not the Senate or the Council, are we? Ready when you are, Obi Wan."
Obi Wan felt a surge of gratitude. Anakin was loyal, and a good friend. But that wasn't what he wanted from his former Padawan.
"I will hear quite enough from Master Yoda without involving you," Obi Wan said."Let's keep the level of uproar to merely enormous, shall we?"
Anakin shook his head.
"Anakin, this is my burden to bear," Obi Wan said. "I appreciate your wanting to help, but I must do this alone."
Anakin gazed at Obi Wan, saw he wouldn't change his mind, and nodded unhappily.
The cartoon had to delete this scene because there isn't enough time.