This problem might occur when you have a virus or a trojan. Please check the issue by carrying a virus scan and also get a trojan remover in order to get free of the trouble.
Yet the regsvr.exe could have been deleted by your anti virus software itself for the fact that it had been infected. In such a case, you will have to get the file back.
Still your computer might be having no problem at all. It might happen in the situation that there is a malicious prgram that is tricking you.