I was getting this message when I opened LB-LINK Sim Modem software on Mac
The application “HSPA USB Modem” can’t be opened. -600
The problem arises because you have closed the application but it is still running in the background. I was not able to find exactly which background task to kill to fix it but you can simply logout (with do not open current windows) and log back in, the error should go away.
By the way, the software for LB-LINK USB MODEM does not work correctly on Mac (It does work on Windows), looks like the mac applications are buggy, at least for now.