Delete files from directory inside Document directory?

Two things, use the temp directory and second pass an error to the fileManager.removeItemAtPath and place it in a if to see what failed. Also you should not be checking if the error is set but rather whether a methods has return data.

func clearAllFilesFromTempDirectory(){

    var error: NSErrorPointer = nil
    let dirPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as! String
    var tempDirPath = dirPath.stringByAppendingPathComponent("Temp")
    var directoryContents: NSArray = fileManager.contentsOfDirectoryAtPath(tempDirPath, error: error)?

    if directoryContents != nil {
        for path in directoryContents {
            let fullPath = dirPath.stringByAppendingPathComponent(path as! String)
            if fileManager.removeItemAtPath(fullPath, error: error) == false {
                println("Could not delete file: \(error)")
            }
        }
    } else {
        println("Could not retrieve directory: \(error)")
    }
}

To get the correct temporary directory use NSTemporaryDirectory()