regsvr32 doesn't work on my winXP admin account

Question

Summary

regsvr32 fails with code 0x80004005 (E_FAIL - Unspecified failure) on my admin account, but works on Administrator account.

Previously I didn't have this problem.

Full question

Recently, I have noticed some problem on my PC:

• I couldn't install PowerChute v3

  According to the FAQ, the fix was

  regsvr32 vbscript.dll
  

  However, running that on my admin account failed with this error

  DllRegisterServer in vbscript.dll failed.
  Return code was: 0x80004005

  According to Microsoft, 0x80004005 is means "E_FAIL - Unspecified failure".

  Surprisingly, it worked when I ran regsvr32 as Administrator account.

• "Edit with Notepad++" entry in context menu disappeared.

  Thanks to this thread, I found that the solution was

  regsvr32 NppShell_06.dll
  

  Similarly, it also failed with error 0x80004005 on my admin account, but worked on Administrator account.

  Now, each time I install a Notepad++ update, I lose the context menu entry (unless I install the update as Administrator). This didn't happen some time ago.

• I couldn't install my HP printer network drivers.

  HP installer didn't give any error code.

  After several attempts, I thought the cause could be regsvr32.

  So I tried running the installer as Administrator, and it worked.

• My APC UPS is not always recognized.

  When I boot my PC, the device manager shows a warning and says

  This device cannot start. (Code 10)

  Sometimes it works if I unplug and replug the usb wire, or if I disable and enable the device, or if I reinstall the driver. But most times it doesn't work.

  However, it always works on another computer.

  I suspect the problem is also regsvr32.

How can I make regsvr32 work again?