Cloaking Issues

[ODanial]

I really need some support on this, but I'm not sure if I'm missing something. At first when I began playing, as an Infiltrator I could cloak at any time as long as the meter was charged. There were no problems to begin with. Now after playing a couple of more times I can only seem to cloak on the first few lives and after that pressing the F key results in an error sound. I've searched the internet and the forums but nobody else seems to have this issue. Thanks in advance.