In the C:\Windows\Registration folder there are usually two .clb files (R0000000x and R000000y). Before the Win XP SP3 one of them was undeletable, I know it because I used to delete the new .clb files that they were sometimes produced and so I had also tested the old ones. After installing WinXP SP3 (at least that's it when I noticed it) they all became deletable. I experimentally deleted them and a new one R0000001.clb was automatically produced. "All right," I thought, it is a new fresh one and it starts counting from the begining". In fact I really had no idea what these files were. I payed my experiments with an early format (I had reformated some days before.This files have the security informations for the COM+ elemants.I didn't know it. One more thing that I finally discovered is that the newlly produced files after the deletion of the original ones were corrupted. The problem appeared when I tried to use NTBackup to make a safety backup of the System's State. At least in my case it worked, but without using the MS Software Shadow Copy Provider Servicethat failed. In the event log I found an error report from VSS (Volume Shadow Service) about not being able to create a COM+ instance for the service with CLSID {xxxxxxxxx}- it was the VSSVC service as I fount in the registry which is the only component of the COM+ registration of the MS Software Shadow Copy Provider Service, wich was missing. I searched in the web and found no solution. I reformated, had the same problem again and this time I realised that the problem was the corrupted .clb files. There is always a possibility that this files get corrupted without being deleted and replaced- however the system itself does this from time to time.If you have problem with the COM+ elements and especially the MS Software Shadow Copy Provider Service you should consider this possibility, especially because if this is the case nothing else will help but transefing the good .clb files from another computer.The problems that you may have vary, the MS Software Shadow Copy Provider Service may disappear from the COM+ elements manager panel (Microsoft Management Console), it may not contain the VSSVC element (which lets it empty and useless) or it may just not be working. You can also find various relevant errors in the event log, the common symptom however is that you can't start the mentioned service neither from the Services management console nor from the COM+ elements one. How to solve the problem Close the COM+ console if you have opened it and reboot. Copy the two .clb files of a computer which works normally to a CD or whatever you want and transfer and paste them in your computer's C:\Windows\Registration folder. Delete any existing others. Now open the COM+ elements management console. The MS Software Shadow Copy Provider must at least be visible and contain the VSSVC element. If it still isn't visible "play" with the "Advanced" options in the "Properties" sheet of any of the visible COM+ elements. There are two options: "Not allow changes" and "Not allow deletion" Leave the second one alone and "play" with the other. It must normally be activated in all the elements, check if there is one that doesn't have it checked, check it and press OK. If they all have the no changes option checked just uncheck it in one of them and then check it again. In this way there will be a kind of reffresh and all the unvisible COM+ elements should become visible.If the MS Software Shadow Copy Provider element is visible from the begining or gets visible but it is still empty (no VSSVC content) just delete it- don't worry, it won't really be deleted- , reboot and follow the same procedure. When finally the service will apear in the COM+ console and contains the VSSVC element it may still not work- try to activate it. If you can't uncheck the "no changes" option in its properties, check the several tabs of it and make sure that it is configured to run as a server- with the "Run as NT" service checked and with the System Account. Try to activate it again, now it should run. Remember that you need healthy .clb files from another computer, without them you will just waste your time. If the system deletes one or the two of the transferred .clb files you can reserve them as far as anything is working allright, however a backup of the transferred ones (made before the rest of the procedure) could be usefull. This is the way that I solved my problem. I hope that it will be helpfull for others too. If you have problems with the MS Shadow Copy Provider Service and you can't find a solution I think that it's worth a shot two try this, even if you haven't deleted the .clb files as I did. And a last advice: Don't play with this .clb files. If you delete one of them (surely if you delete the two or all of them if there are more than two) you may have a big trouble. The system can reproduce them but not correctly. Whishing again that my experience will be helpfull for others.