Are you trying to melt in a double boiler or microwave?
If you are using a double boiler, be sure you don't get any water/steam in the chocolate.
If you're using the microwave, it works best at about medium power.
In either case, you should stir frequently--the chocolate doesn't change shape when it melts, and it is easy to overheat it, which will make it thicken again.
RedPanda
NOT ONE DROP OF WATER!! Your chocolate will seize.....
Add shortening. If it is getting thick, you are probably burning it. Only heat it 30 seconds at a time in the microwave and stir each time in between. Water, even a drop will kill it, too. I use paramount crystals, which is like crystilized shortening to thin out my chocolates for coating, but regular crisco works in a pinch.
p.s. thereason to add shortening instead of butter is because butter is ctually 20% WATER...... remember.....WATER AND CHOCOLATE ARE NOT FRIENDS. 
I just made cake balls tonight, also. I did not have any liquid coffee creamer, but I did have powdered. I used French Vanilla cake scraps that I actually flavored with butter rum, the coffee creamer was cinnamon vanilla, then I added a splash of Kahlua and Amaretto until it made a ball. I put a little too much in, so in trying to find something to dry it out with, I found a box of Corn Flakes in my pantry. I ground them up in my food processor and added them to the cake ball mix. I really like that little bit of crunch! I used cherry flavored red chocolate and plain vanilla white chocolate to coat them. I honestly have never made cake balls before, although I have eaten them! 
Not too bad for the first time!
I'm glad the oil worked out for you! That's good to know for reference.
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