Here is a position I often adopt myself, and encourage others to:
It may not be your fault, but it is your problem.
You are paid a salary. Your company does that because it gets value from you. There are lots of ways you can provide value:
- you can work on billable projects after sales has landed them
- you can represent a valuable asset that would be hard to re-acquire if a big project came in (I've paid people for months so I would have them if I needed them later)
- you can be a name (and skill list) on a list of people that sales has, that they use to prove why they should get the billable project
- you can contribute to things that sales has to do to land a project
- you can make the workplace nicer or more efficient
- you can (less than brilliantly) help others with things that are out of your scope, not as well as them but better than sitting around doing nothing
- you can learn how to do new things in order to expand that list sales uses, and to increase the things you can help with that used to be out of your scope
- you can try to help the company land billable work (speaking at user groups, networking at industry events, keeping an ear out for things to bid on)
It seems like you're not willing to go past #3 on that list of possible values. If 1 and 2 are enough, perhaps they'll keep paying you to do nothing. I wouldn't count on it, though. This has nothing to do with "fault" or "blame" - if there isn't enough billable work for point #1 to count for much, and your value stops there, then your value falls below your salary. If there is someone else in your group who is willing to help sales, to help the other department, to do some boring admin stuff, then I would keep that person and get rid of the person who has less value - you.
If you don't want to be the person who has less value, start having more value. It's not your fault that there isn't enough billable work for #1 alone to justify your salary right now. But if you lean back in your chair and declare this lack of billable work to be "not your problem", you may soon find that coming up with your salary every month is not your employer's problem any more.