I have too
I was getting this error with the 3.0.0-alpha.1 version of the pod (Xcode 8 GM). Updating the pod to 3.0.0-beta.1 fixed this issue for me.
I have too with 3.0.0-beta.1
Use 3.0.x and Cocoapods 1.1.x
@AleLudovici I used 3.0.0-beta.1 in CocoaPods(1.1.x) and Xcode8 version (not GM).

I am using cocoapods: 1.1.0.beta.2
Xcode: Version 8.0 (8A218a)
Swift 3.0
pod 'RxSwift', '~> 3.0.0-beta.1'
pod 'RxCocoa', '~> 3.0.0-beta.1'
@leizh007 ,
please try with 1.1.0.rc.2.
Ok guys, this is a dupe of #899, let's continue discussion there.