Possible crash issues and solutions...
Steam game -
Make sure it is updated. The steam version had a bug that has been fixed.
Mods -
Once a mod has been installed and you use it in a city, if you don't delete that plot in the city (building, texture, ect) and delete the modded .pak, the city will not be playable. Delete all mod buildings before deleting the pak.
Blueprints -
The game keeps a record of what blueprints have been placed EVEN IF YOU DELEAT THEM! This means that if you use a modded one and delete that mod from your pak folder then try to play your city again, it will crash.
Goldiva has posted a way of fixing this.
Goldiva wrote:I occasionally get the typical DBGhelp.dll crashes but it's not such a big deal as it tends to happen long into the game. However yesterday I started getting the "crash upon loading" problem with my 750,000 main city. Autosave and all 5 previous checkpoint saves all crashed upon load. I thought I have lost my main city forever. After much testing I have managed to load the city again. The offender/ culprit =
C:\Users\YourUserName\AppData\Local\Focus Home Interactive\Cities XL 2011\live\offline\solo\solosaveregion00map00\auto\bp.CXL
It seems the "ghosts of past blueprints" are causing the crash (in my case), which happen at the end of loading city or a few seconds after city load.
This bp.CXL contains 3 STAGE ONE blueprints that I plopped earlier then deleted. Yet the ghosts remain. So I manually deleted these suspects then launch game. I got my main city back, and playable as usual. So far so good.
The same "bp.cxl" file exists in other checkpoints folders in this city. Somehow (in my case) deleting only the bp ghosts from the bp.cxl autosave version does the job. I purposely leave the other bp.cxl files with bp ghosts in there to see if I could continue to play without issue. If so the real culprit is most likely the autosave.
The bp.cxl file in my 23/11 checkpoint1 contains only the first bp ldnmilleniumwheel which I plopped/deleted many days ago. Prior to 28/11 I haven't experienced any crash on load issue. On 28/11 I tested two user modded BPs, desalination and sydneyoperahouse (karel's). These two BPs were also plopped and deleted then removed from my pak folder, yet their ghosts remain. So this "crash due to BP ghost bug" could be uniquely related to (some?) modded BP's ghosts. However, as I don't build original BPs in my cities I can only guess if the original BP ghosts also cause permanent crashes. In any case, "BP ghost in bp.cxl" is a confirmed bug.
For those who wish to test if this resolves this crash on load issue - I use Notepad++ to open and delete the bp.cxl ghosts from the first <tab> to last </tab>, save, then launch game. Careful so you won't accidentally delete the blueprints you built and want to remain. *See eariler pg3 Focus tech team post in this topic how to unhide Appdata folder if you can't find that folder. Do feedback here if this workaround applies or not in your case. Good luck in saving your cities!
For tech support ref: my system: Dell Prec/Win7/64b/12G/QuadroFX1800.
Meanwhile I feel BPs, as they are, are really not worth the precious game time and trouble they cause. I'm slowly converting all BPs into Landmarks and Leisure buildings to my own specs.
AutoSave corruption -
This method works for cities that have a manual save available ONLY! If you only have autosaves, this will not work.
Delete the autosave folder - C:\Users\username\AppData\Local\Focus Home Interactive\Cities XL 2011\live\offline\solo\solosaveregion*\auto ( * is whatever city number it is)
To identify what city to delete, open the city.cxl file in the solosaveregion* folder and look twords the bottom for this ( <itm key = 'CityName' value = 'YourCityName' /> )
Deleting the auto folder will set your map back to default before the city was built.
Load up the game.
Load up the city, and don't panic when nothing is there....
Go to the save area and load up the latest manual save you have.
PRESTO! you have only lost some of your city, not all of it.
Manual save often (I save on the hour, every hour)
User file corruption -
Move the "Cities XL 2011" ( C:\Users\username\AppData\Local\Focus Home Interactive\Cities XL 2011 ) folder out of place and put it on your desktop.
launch the game
close the game. This will give you a new set of user folders to work with.
Copy the "offline" ( C:\Users\username\AppData\Local\Focus Home Interactive\Cities XL 2011\live\offline ) folder back into the game directory from your desktop copy, replacing the newly created offline files.
Launch the game and play without trouble. This will refresh your user data without loosing your cities.
*.dll issues -
Update your graphics card drivers
Update your sound Drivers
Do a fresh reinstall of Windows 7, Vista, XP.
Contact customer support.
.dll files are system files and if they are corrupted, they must be repaired. A new driver or operating software update will fix most of these issues.
64 bit system issues -
The game is still just a 32 bit program, and is therefor limited to 2 GB of ram.
Zooming all the way out or all the way in may cause issues.
Taking high quality screenshots of large cities cause issues.
the virtual memory can not handle the load.
It is something that needs to be patched...
system requirements -
If your system doesn't meet specs, it is not a problem of the developer that it is not stable. Update your hardware.
Other solutions -
Reinstall the game
make sure it is under administrator privileges
run in compatibility mode for a lower level operating system.
And wait for the PATCH!
If you have other methods that have worked, feel free to post them here and I will add them. Happy rebuilding!
( I think i just lost my 1.5million hab city like the three other one before. Getting tired of starting new city hoping that this one won't crash like the other ones. Big waist of time. 10/10 for the game while it works. 0/10 for waisting time again and again
I've tried almost everything posted in the opening post, NO RESULTS whatsoever 
Off course, I was pretty pissed at the game since I wanted to play it. I've lost a city before, wouldn't wanne loose another one. 
