A minor issue but its not mentioned anywhere so I decided of writing about it.
Linux users may come accross an issue of not able to download from some users and also that their PM dont reach to some users. That happens due to the mismatch between the character encoding used by your client (UTF-8) & that of the HUB (if on windows, uses CP1252).
In my case, the HUB server runs on windows machine so they were using CP1252 encoding and I use linux, which uses UTF-8. So, there is a mismatch here.
Changing the character encoding in settings of eiskaltdcpp solved the issue.
Below screenshots show you where do those settings lie in Eiskaltdcpp (Its my favourite dc client on linux).