I have been reading similiar difficulties in installing the 2.75 mod, and have found that I too cannot install the mod correctly. So, I started from scratch, uninstalled my MtW2 game and erased the files, then re-installed Medieval II Kingdoms Gold Edition.
After a clean MtW2 install, I then downloaded a fresh Ren2.75 rar file for the mod. I was careful to install to destination folder:
C:\Program Files\SEGA\Medieval II Total War
I realise the exe mod file will create its own Renaissance folder as it installs. I removed any attempt of the exe file to add a "Renaissance" or "Renaissance2.75" to the destination path. The error message I got was " cannot open/create uninstall.exe file" - the install was then aborted.
I ran the install exe file again, and got a second error message "cannot open/create ren.bat file".
I even tried running it as Admin but got the same errors.
With some mods for RtW, I have to extract the files by hand and paste them myself. I installed the files from the ren.exe file to my desktop, which was a Ren2.75 batch file and the main Ren Total War 2.75 folder (I renamed the folder to just Renaissance). I then removed the Ren .bat and .cfg files and put them into my main MtW2 folder.
Unfortunately, the game loads into normal MtW2. I assume that the problem is an io problem in the config.txt, so I changed the txt to only this:
[io]
file_first = true
[features]
mod = Renaissance
[game]
advanced_stats_always = 0
advisor_verbosity = 0
ai_factions = skip
allusers = 1
auto_save = 1
blind_advisor = 0
campaign_map_game_speed = 10
campaign_map_speed_up = 0
campaign_num_time_play = 184
chat_msg_duration = 10000
disable_arrow_markers = 1
disable_events = 0
english = 0
event_cutscenes = 1
fatigue = 1
first_time_play = 0
label_characters = 0
label_settlements = 1
micromanage_all_settlements = 1
morale = 1
mute_advisor = 0
no_campaign_battle_time_limit = 1
pref_factions_played = 40474
tutorial_battle_played = 0
tutorial_path = norman_prologue/battle_of_hastings
unit_size = normal
use_quickchat = 0
It still loads into normal MtW2
Sorry for the long-winded explanation, but I wanted to be specific as to the overall installation problem. Any help would be greatly appreciated>