No Exec line in the session file: ubuntu. Running the GNOME

[Brianivander]

No Exec line in the session file: ubuntu. Running the GNOME failsafe session instead.

I got this message when I'm booting into Linux MInt 14 Cinnamon 32 bit.
I did something to my computer before:

I wanted to multiboot Linux OSs. And I wanted to make the linux OSs can share the files in one partition. So what I did is

I installed the LM14 first, by dividing some partitions into:
/
/boot
/home
swap

It works fine. No problem with the LM14.
Then the other OS that I want to share files with is Ubuntu 12.
I install it into new partitions for Ubuntu:
/
/boot
and I select the LM's /home partition then I mount it as /home without formatting.
Then I continue the installation and reboot.

Then came this message:
No Exec line in the session file: ubuntu. Running the GNOME failsafe session instead.

so I click Ok, then another message appeared:
This is the Failsafe GNOME session. You will be logged into the 'Default' session of GNOME without the startup scripts being run. This should be used to fix problems in your installation.

Then I click ok, then another message appeared:
Failed to load session "ubuntu"

Then there is only one button: Log out. So I click it and got into Log in screen. And when I had put my username and password, there is a message asking to run xClient or something like that. Then there were three buttons: Make default, cancel, just login. So I chose just login.

Then I found out Some good things:
1. That I did make the /home partition mounted in both LM14 and ubuntu,
2. The settings of Firefox were applied in both OS, the bookmarks, history, and skin.

But the problems are:
1. There is always those message appeared when I am booting into LM14
2. The Ubuntu Theme is changed into Mint Theme, but with some adapting. So it looks bad. Then I changed it back to Ubuntu Theme. But when I boot back to LM14, the Theme changed with some adapting, I guess it's because I changed it in Ubuntu, and it looks ugly.
I guess the Themes setting were put in the /home partition so it affects everytime I change. Is it right?

My question is:
1. How can I make the same /home partition to share files , but seperate Themes setting between those OSs?
2. How to fix those messages?

Thank you so much for the help.

Brian

[Brianivander]

And here is my computer spec:

prawira@prawira-PC ~ $ inxi
CPU~Dual core Intel Core i3 CPU M 350 (-HT-MCP-) clocked at Min:933.000Mhz Max:2266.000Mhz Kernel~3.5.0-17-generic i686 Up~1:02 Mem~434.4/1880.2MB HDD~321.1GB(1.6% used) Procs~154 Client~Shell inxi~1.8.4
prawira@prawira-PC ~ $

Linux Mint
Release 14 (nadia) 32-bit
Kernel Linux 3.5.0-17-generic
GNOME 3.6.0

Hardware
Memory: 1,8 GiB
Processor: Intel Core i3 CPU M350 @ 2.27GHz x4

System Status
Available disk space: 117.2 Gib