When u want to add manually a download and click "+ADD" button, TIXATI freezes for 10 seconds the 1st time, and about 2 seconds next times until restart Tixati.

It is not a new problem. I'm using tixati on portable mode, on another Drive (d:).

You suffer from paging on the system. If you are using a machine with larger RAM (> 4 GIB) switch to the 64 bit Tixati.
If you are already running 64-bit you need to stop running so many programs concurrently with Tixati. I schedule my downloading overnight on Tixati while I am not gaming or streaming.
Since the access is not directly tied to your configuration (.dat files) this situation cannot be remedied with a ramdisk like many other thrashing problems.
As a frame of reference I use 3 GiB of RAM with 8000 transfers using about 3 GiB of virtual RAM, 1100 MiB physical RAM. Tixati is not known for being a low resource usage program.

what OS?

what version of Tixati?

what tab does the add window open on?

does it hang for all of them?

do you have network drive it has to look for, or something like that?

I also am having this issue, I am not suffering any sort of CPU or RAM shortage, and I am running Tixati v2.71, 64-bit Windows Build
This happens when I click + Add and it'll freeze for almost exactly 10 seconds.