Sporadic issues - transferring album to my iPod touch

I have an iPod touch, and when I buy a new album on iTunes, I can usually highlight all the songs and drag it over to download to my iPod. Occasionally it doesn't work. I will attempt to do this with the same album multiple times and it won't work. I checked and the album is downloaded in iTunes. I deleted the download, and re-downloaded it and that still didn't work. I have storage space available on my iPod. I don't want to set up to automatically sync because I have music on my iPod that isn't on my current laptop's iTunes program. Does anyone have any advice? Thank you!