Xcode failed to download, use the purchases page to try again I continue to get this error each time I try to install xcode:
"Xcode failed to download, use the purchases page to try again"

This is with the newest OSX 10.10.3.

I found this thread:
Xcode failed to download. Use the Purchases page to try again

I tried the two possible solutions:
1) Resetting the App Store app via "Debug --> Reset Application" does nothing as far as I can tell (there's no visual feedback that selecting that option does anything).
2) I tried to find the plist file in /private/var/folders/, but the directory there is empty.

I've tried deleting xcode, reinstalling, etc, etc.  I found this crash report via system log which...seems bad...seg fault?:

Process:               softwareupdated [711]
Path:                  /System/Library/CoreServices/Software Update.app/Contents/Resources/softwareupdated
Identifier:            softwareupdated
Version:               744.10
Code Type:             X86-64 (Native)
Parent Process:        launchd [1]
Responsible:           softwareupdated [711]
User ID:               200

Date/Time:             2015-04-10 10:00:00.603 -0700
OS Version:            Mac OS X 10.10.3 (14D131)
Report Version:        11
Anonymous UUID:        &lt;redacted&gt;

Sleep/Wake UUID:       &lt;redacted&gt;

Time Awake Since Boot: 7300 seconds
Time Since Wake:       980 seconds

Crashed Thread:        11  Dispatch queue: com.apple.SoftwareUpdate.SUCatalogDataManager.Handler

Exception Type:        EXC_BAD_ACCESS (SIGSEGV)
Exception Codes:       KERN_INVALID_ADDRESS at 0x000000012f939380

VM Regions Near 0x12f939380:
    MALLOC_LARGE           000000010c43f000-000000010d293000 [ 14.3M] rw-/rwx SM=PRV  
--&gt; 
    JS JIT generated code  00003bb82f600000-00003bb82f601000 [    4K] ---/rwx SM=NUL
I encountered this problem many times, and I found today that it's caused by lack of disk space.

In my machine there is more than 7GB spare space, and after downloading the files, it reported this error.

Today I find the real problem from /private/var/log/install.log, it is caused by low disk space, so I made more space, and the update succeeded.

Since the download is 6 GB you'll want to delete old versions and have at least 15 GB free space before trying again to download. Look in /var/folders for paused / stuck downloads as well as perhaps cleaning any local time machine snapshots once you delete a large app like Xcode. Even after emptying trash, it will consume space for a few days or longer if you don't regularly have a Time Machine volume attached to let the snapshots age out.