Treyarch and Activision’s “Call of Duty: Black Ops 2” launched on Tuesday, but the next “Call of Duty” installment wasn’t the only game some buyers received. In a bizarre accident, some PC editions shipped with code from BioWare’s “Mass Effect 2.”

A number of reports from fans indicate that some PC copies of “Call of Duty: Black Ops 2” carry a second disc which appears to come with code for “Mass Effect 2.” This bug has prevented some players from continuing the game on the PC since the second disc that was intended to come with the game is missing.

“Buy Black Ops 2. Put in disk 1, installation going swimmingly. Asks for disk 2, so I comply,” wrote one user called Krackerjax in Steam’s official forum. “It is read as a disk for Mass Effect 2, can’t install game. What on Earth is going on?”

The post was followed by a thread of replies from other fans, some of which who said they encountered the same problem.

“Nope, he’s right,” replied user richei. “The same thing happened to me and I just checked the files. The 7gig [GB] file is listed as ME2_RTP and the other 2 are autorun and autorun. But you know, I’m not all surprised this happened. So either someone put the wrong file on there or they named it wrong, who knows.”

The issue appears to be exclusive to PC players. The game discs which carry “Mass Effect 2” code are still labeled with a “Black Ops 2” cover mount, indicating that this is a problem with the way the disc was manufactured.

The error isn’t entirely surprising, as game publishers such as Electronic Arts, responsible for the “Mass Effect” franchise, and Activision may share manufacturing facilities. User Donald Theriault noted this possibility when discussing the issue on Twitter.

“This is why Nintendo controls their disc printing,” he tweeted, along with a link to an article about the issue.

Activision has yet to comment on the matter.

Despite this manufacturing bug, “Call of Duty: Black Ops 2” became Amazon’s most pre-ordered game. The online retail giant made this announcement on its website just two days before the game’s release date on Sunday:

“Black Ops II broke records and is now our most pre-ordered game ever! Pre-order to get Nuketown 2025 Bonus Map.”

The company has not disclosed any specific sales figures for “Black Ops 2.”

See the video below to get a glimpse of what some PC gamers are experiencing. Have you been effecting by this problem? Sound off in our comments section.