Ive already download 2 copies of WinRAR x86 (32 bit) 3.90 beta 4 separately from WinRAR archiver, a powerful tool to process RAR and ZIP files and WinRAR - Free software downloads and reviews - CNET Download.com , keep on installing and uninstalling..but still the error message " The archive is either in unknown format or damage" ..meaning that the software works fine...so the file itself or the method to download it is wrong..

For my case, i don't know whether it will work with others...
Try NOT to download it via download manager..I'm using Free Download Manager V 2.5 build 758..
Instead use the normal aka slow ones which is included in your internet browser IE mozilla Firefox..
Noticed that the file name is different when using download manager and the normal download..below the examples

SeKelPer 1.0 <---- Normal download
53233d1201704884-isakas-ashi-kuskus_osentogg-sekelper-1.0 <-- Using Free Download Manager

Surprisingly the files from the normal download ones is in perfect order..

so Fairose maybe u can try this and I'm sorry if it doesn't work for you..