Strange as it may seem after the game being played for so long, but I think I may have found an issue.
If you trade in a power-up for cash $, it is not possible to use the money to buy a new tower untill you kill the next creep. (in other words, the ribbon(s) around the new towers in the designated section of the screen do not turn green).

It is quite strange that you can make immediate use of the money to upgrade a tower though, so I suspect that it is just a matter of triggering the right event to fix it.

Thanks for your attention,

MainstreaM

i'm quite sure it's just a display issue.
you can select the tower by mousclick ant it will place it.

If that was true, my friend Lord, I wouldn't have posted it.

I don't know if you can select with numbers - number selection doesn't work for me anyway - laptop users are disabled people, you know :( But that's another issue :$

Why are we laptopper disabled? I play on a laptop he only thing I lament is that I have no numpad. But, where is the problen? I still have the bar with numbers.

Number bar does not work for Dutch azerty keyboards... that's the point ;-)

Ya, that must be just a display issue. I'll have that fixed for the next version. Thanks for letting me know.