This is the dilemma of contractors too, who enter the job with a well-defined skillset. Over time you become 'siloed' leading to a narrowing range of opportunities as all software eventually becomes obsolete and the demand for it falls away; and, it seems at a faster rate than ever. Very rarely do clients put temporary staff onto courses: if you're lucky, you can pick up peripheral expertise or an exceptional opportunity arises. We know that if you've managed to learn a set of skills over your career, then picking up a few new language or package isn't really a big deal. Clients aren't interested though. In the current job market, there always seems to be somebody who has all your skills, plus exposure to that one business application you've never heard of.

What do you do? Getting the next job isn't just about technical expertise. The ability to 'get on' with your team is now regarded to be just as important. This soft skill doesn't come easy to a lot of people. But look on it as a new language. And the good thing about this new language is that you can start using it in your current job right now and then add it an an extra skill in your resume.