What is reasone for "searching DHT...." error and how to fix it..?

You mean the orange "Searching DHT..." text flashing in Status column on transfers view? It isn't error, this message informs that Tixati searches "Distributed Hash Table" for peers to connect. This usually happens every half an hour, it is normal for public torrents.

but what if it reoccurs over and over again, never reaching the download stage? this problem returns all the time lately, no matter which files i try to download, even when i download something with plenty of seeders and leechers.

Same problem here, downloading 0 of 0 files shown as well?

Try downloading torrent file instead of magnet link. Read Optimize Tixati help guide, step 3. is about DHT related problems.

OMG what is wrong with Tixati, since the last update Tixati Keep Saying Port Unconfirmed, Port Unconfirmed, Port Unconfirmed,Port Unconfirmed,Port Unconfirmed every 5 min.. i can't download with my fulll speed, and people can't get files from me with fully upload speed, this is soo annoying :(

Know it's kinda a while later, but while searching DHT isn't exactly an error, it's caused by leechers usually past what you can handle, as most torrent programs default start seeding which ruins your own download times in cases like this. For Tixati praise the sun you at least have the option to say screw those leechers, best way to fix the DHT freezing up a download is under where it shows your download progress there's a peers tab, hit that and right click all the addresses there (except yours) and select "Disconnect" now if they're botted downloads (which usually you can tell because they are China or Russian addresses) they will continue to force connect themselves every second or two thus slowing you down even more, thankfully Tixati has something for that too, you should've noticed a "Force Choke" selection box when you did the disconnect, select that and it'll basically do what it says, and Choke their connection, forcing it to drop without effecting you any further.
Doubt the original person who ased the question is still visiting here 3 years later, but hope this helps anyone else having problems with the DHT connection trying to force itself.