Unable to remove Trojan D.loader/LX warning message

Dear all. My computer was infected by spyware. After installing "Spysweeper" problem seemed to be solved.No spyware found. And no virusses detected by CAsecurity (anti-virus).I tried other anti-virus programs to do a scan, computer is virusfree. But now I have a "pop-up" that appears every few seconds. It says that I have a Trojan in my computer and that they strongly recommend "Spyknight" or "Spysoldier" to remove the virus. Can anybody tell me how I can block this pop-up? Apparentely it comes from the "inside" of my computer. I am using Microsoft Xp. Many thanks!

 

Spysweeper, spybot nor Adaware is able to trace or remove this pop-up....I tried them all with no result..?

 

Ewido anti-spyware (Avg) did the job!! Thanks for the tip!