Samsung is living through its worst nightmare with its recently released Galaxy Note 7: the South Korean company had to recall 2.5 million devices, halt sales in 10 countries and has seen its stock prices fall by 10 percent in the aftermath of its voluntary recall. The root of the problem, according to Samsung’s preliminary report to the Korean Agency for Technology and Standards, is a production error.

In the report, Samsung shares its initial findings: an error in producing battery cells resulted in negative and positive battery poles to come in contact with each other leading to excessive heat. The company did note; however, that more research needs to be done to find “the exact cause” behind the battery mishaps.

When Samsung first issued its recall,  the company cited 35 cases of Galaxy Note 7s overheating or exploding. Koh Dong-jin, president of Samsung's mobile business, told reporters in a news conference that an investigation revealed “a tiny problem in the manufacturing process so it was very difficult to find out.”

The issue, reported The Associated Press at the time, is with a battery cell produced by one of Samsung’s two battery suppliers. According to Bloomberg, the main supplier for Galaxy Note 7 batteries was Samsung SDI Co.—Samsung’s sister company. For the new devices, reports ZDNet, batteries will be sourced from China’s ATL, which was the company’s secondary supplier.

In light of the battery problem, which impacts 0.1 percent of devices, the company has advised owners of the device to shut off their devices and “exchange them as soon as possible.” Meanwhile, the Federal Aviation Administration has urged airline passengers to not use or charge their Note 7s while on an aircraft and in the U.S., the Consumer Product Safety Commission has warned users to “power them down and stop charging or using the device.”