"richtx32.ocx" is not an executable file and no registration helper is registered for this file type.
I had this thing always appearing while using my FTP software so I had to fix it. I looked all over the internet to find any possible fix but no one gave me the answer I was looking for. After a while I decided I would try to find out the latest version of this file and almost every place I went to, I found the version 126.96.36.199 which was the one not working for me. Then I went to http://www.martin2k.co.uk/ and grabbed his Microsoft Rich Textbox Control 6.0 (SP4) (richtx32.ocx) which was version 188.8.131.52. By executing
regsvr32 c:\windows\system32\RICHTX32.OCX on my winXP computer, the damn thing finally registered itself!