PVC's and generic Toprol XL or generic Lopressor?

I am trying to find the cause of the PVC's that I have had since November, which have gotten worse.  The past 10 days I have had them constantly at 1200 per hour and feel terrible.  The dr. wants to do an ablation.  On searching the internet, I came across alot of message boards that say that alot of people have had many side effects, including arrythmias, when they were switched from name brand Toprol XL to the generic version.  I was on Toprol XL for over 10 years with no problems.  I was switched by my drug company last October and the PVC's started in November.  In Feb, I was switched again to generic Lopressor, which from what I heard, is the same things only not extended-release.  Has anyone experienced problems with the generic form of either drug or have heard of others having problems?