No one got any idea why this is happening?
The button is a Symbol and the size has been changed at some point.
I just looked at your file, to correct it
- double click the btnRollover symbol in the Symbols Panel
- at the symbol Stage properties, turn off 'proportional' size by clicking the link icon;
- then set the w to 237 and h to 51;
- then exit Symbol Edit mode.
Indeed it could be tricky to determine what may have happened for the resize to occur down to a 1px width. One possible scenerio, and I have done this myself, is forgetting to deselect the 'proportional' link property.
Certainly something to keep on eye on.