Do you have secure Dimensions in that cube?
How was the data changed:manually or using planning function?
It looks like in AO and in EPM errors are coming from different places.
In BW 7.5 SP03 I don't that Method that breaks in AO at all.
You can try putting a break-point in Method that breaks in EPM. It looks like another LUW is open when you are truing to save.