If you didn't change anything - the story is "It should work" - try this;
Select every item in the feature tree and suppress them, then one by one un-suppress each part and sub-assembly. Somewhere there is a circular rebuild & and if you can move it after doing the above and then when you open the assembly again and it does the same thing, then the assembly has circular rebuild issues..
I did as suggested and then when all were Un-surpressed the Cam functions returned to normal .
Still not sure of what happened, but i now know what to do next time.
I am sure I did a rebuild before saving last time, but ?
A big Thanks John !