Reappearing keys

Hi,

using CCleaner ver. 2.21.940 on Windows 98 SE I found that some registry keys reappear after deleting them. These are the keys:

c:\cubasisd\cubasisd.exe %1 HKCR\midfile\shell\open

C:\DBASEWIN\bin\dbasewin.exe %1 HKCR\.prg\shell\open

C:\DBASEWIN\bin\dbasewin.exe %1 HKCR\.wfm\shell\open

C:\DBASEWIN\bin\dbasewin.exe %1 HKCR\.dbf\shell\open

C:\DBASEWIN\bin\dbasewin.exe %1 HKCR\.qbe\shell\open

C:\DBASEWIN\bin\crw.exe %1 HKCR\.rpt\shell\open

c:\cubasisd\cubasisd.exe %1 HKCR\.all\shell\open

c:\cubasisd\cubasisd.exe %1 HKCR\.arr\shell\open

Cubase is NOT installed on my pc, nor DBasewin (I really don't know where this came from). I've deleted those keys many times with CCleaner, but every time I do a registry scan they are still in. I've tried to delete them by hand with Regedit, but it was useless. A system scan with Avast and Spyboot give no result, apparently there's no virus, trojan or spyware running...so, what's the problem ?