I had exactly the same problem.
I sprayed the bush with 'Provado' in May and then again in September (2011). I only use Provado when I have to as its terribly strong (don't get it in your eyes).
The Viburnum bushes are now fine and there has been a huge boost in the leaves.
I haven't used the Provado any more ... once treated the beetles stayed away !
Hope this helps and good luck
Chris