Install Xcode: We could not complete your purchase. Unknown Error.

Question

After I upgrade the system to Mavericks, I remove the Xcode.
Then when I use the terminal, the system prompt saying whether to Get Xcode or Get Command Line Tools or something like that. (because I am using git)
Now I want to install the new version of Xcode, but MAS says: "We could not complete your purchase. Unknown Error."
I've tried all solutions out there can be found, like:
1. sign out/back the account
2. remove app store cookies
3. delete the app store cache
4. delete the /var/folders
Nothing works.
I doubt it has something to do with the already working Command Line Tools. But I cannot find this can uninstall it since it is installed alone without Xcode.
Please help.

Answer 1

If you have more than one user account, these instructions must be carried out as an administrator.
Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the icon grid.
Select
/var/log ▹ install.log
from the hierarchical list on the left. If you don't see that list, select
View ▹ Show Log List
from the menu bar. Then select the messages from the last installation or update attempt, starting from the time when you initiated it. If you're not sure when that was, start over and note the time. Copy them to the Clipboard by pressing the key combination command-C. Paste into a reply to this message (command-V).
If there are runs of repeated messages, post only one example of each. Don’t post many repetitions of the same message.
When posting a log extract, be selective. Don't post more than is requested.
Please do not indiscriminately dump thousands of lines from the log into this discussion.
Important: Some private information, such as your name, may appear in the log. Edit it out by search-and-replace in a text editor before posting.