According to Comic REX magazine, Takenashi Eri's manga "Kannagi" will be withheld from publication for some while due to the ill health of the author. It's unknown when the manga will resume publication.

Source: Scan of Comic REX

Edited on Dec 9th=================
The editors of Comic REX magazine officially denied that the suspension of the manga was related to the fans' disturbance. They explained that the sickness of the author was the sole reason for the suspension. Before this official statement, Yuukan Fuji newspaper and ITmedia have already reported that some fanatic fans of Kannagi made the author stop publication.

Source: J-cast News

Edited on Dec 11th=================
According to Minekura Kazuya's (the author of "Saiyuki") blog, Takenashi Eri cannot get out of the bed due to the illness.
The official website announced that the illustrator of the DVD storage box(, which is the extra item bundled with Kannagi DVD volume 3 Limited Edition) will be switched from Takenashi Eri to Kadowaki Satoshi (the graphic art director of Kannagi).

Source: nitro diary
Source: Official website

Edited on Dec 12th=========================
According to Ichijinsha website, Takenashi Eri was hospitalized after finishing Kannagi manga episode released in the December issue and had an emergency surgery. The surgery was successful and she is getting better now. Eri sensei is still in the hospital but she is eager to resume publication as soon as possible.

Source: the official announcement from the publisher