Reason Behind Kim Kardashian's Battle With Old Navy?

As TMZ first reported, Kim filed suit against Old Navy because she felt they were trying to intentionally deceive people into thinking she was a spokeswoman for the company by using a girl who looked just like her in their commercials.

But our sources say ... the suit was filed because Sears felt the Old Navy commercial compromised it's ad campaign for the Kardashian Kollection -- an exclusive line of clothing and bedding that launches in about a month and a half.

We're told Sears execs actually questioned if Kim was part of the Old Navy ads. The company feels the ad creates confusion in the marketplace and that happens to be exactly what Kim needs to prove to win her suit.