Is the combobox that you are trying to attach to very close to the bottom of the screen? If it is not completely visible on the screen, I sometimes get the same error. I had to write an error routine that watches for this and scrolls the screen, then retry the attach.
Of course, if something else is going on, you are going to have to get much more specific about your script and what it does before it can be diagnosed.
The problem was something else. Actually what Inspector shows does not always help you to recognize the ComboBox, instead I did a record & PlayBack for that ComboBox & checked out how it recognozed that ComboBox. Now everything is working.
I generally try to stay away from identifying controls before recording scripts, for precisely the reason you state, and let QARun identify the objects as I am recording. There are those that disagree with me, even in my own group, but the proof is that I spend probably less than 5% of my time manipulating object map items, while others that pre-identify controls spend upwards of 60% of their time manipulating object map items and troubleshooting scripts that have been killed by changing object maps.