Using Wordpress on iPhone 3GS or iPad2 running iOS 5.1.1, I get the error "Couldn't sync posts. Blog returned invalid data." The blog works fine via IE9 on my PC. I am using default twentyten theme on WordPress v3.4 but it is integrated into an X-Cart shopping cart website. As part of the integration, the following rules in the .htaccess file in the root folder.

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RewriteRule ^blog/(wp-login\.php|wp-admin|wp-includes|wp-content|wp-comments-post\.php|wp-cron\.php)(.*)$ blog/$1$2 [QSA,L]
RewriteRule ^blog/(.*).(css|js|gif|jpg|png|html|php)$ blog.php?incl_file=$1.$2 [QSA,L]
RewriteRule ^blog/.*$ blog.php?url=$1 [QSA,L]
RewriteRule ^blog$ blog.php [QSA,L]
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I have run the steps described at http://wpiphonedev.wordpress.com/extra-debug/

The contents of the log produced are below. Can anyone help?

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2012-07-05 06:55:22 +0000 Launching WordPress for iOS 3.0.1...
2012-07-05 06:55:22 +0000 device: iPhone2,1, iOS 5.1.1
2012-07-05 06:55:23 +0000 <WordPressAppDelegate: 0x270780> cleanUnusedMediaFileFromTmpDir
2012-07-05 06:55:23 +0000 <BlogsViewController: 0x28ce60> viewDidLoad
2012-07-05 06:55:23 +0000 <BlogsViewController: 0x28ce60> viewWillAppear:
2012-07-05 06:55:23 +0000 - [Blog hostname] for http://www.marionadie.com/blog: http://www.marionadie.com
2012-07-05 06:55:23 +0000 <WordPressAppDelegate: 0x270780> applicationDidBecomeActive:
2012-07-05 06:55:25 +0000 - [Blog hostname] for http://www.marionadie.com/blog: http://www.marionadie.com
2012-07-05 06:55:25 +0000 <BlogViewController: 0x2bbe00> viewDidLoad
2012-07-05 06:55:25 +0000 <PostsViewController: 0x2c1f90> viewDidLoad
2012-07-05 06:55:25 +0000 <BlogsViewController: 0x28ce60> viewWillDisappear:
2012-07-05 06:55:25 +0000 <BlogViewController: 0x2bbe00> viewWillAppear:
2012-07-05 06:55:26 +0000 <BlogsViewController: 0x28ce60> viewDidDisappear:
2012-07-05 06:55:26 +0000 Error syncing options: Blog returned invalid data.
2012-07-05 06:55:26 +0000 Error syncing post formats: Blog returned invalid data.
2012-07-05 06:55:26 +0000 Error syncing categories: Blog returned invalid data.
2012-07-05 06:55:26 +0000 Error syncing posts: Blog returned invalid data.
2012-07-05 06:55:30 +0000 <WordPressAppDelegate: 0x270780> applicationWillResignActive:
2012-07-05 06:55:30 +0000 <WordPressAppDelegate: 0x270780> applicationDidEnterBackground:
2012-07-05 06:55:56 +0000 <WordPressAppDelegate: 0x270780> applicationDidBecomeActive:
2012-07-05 06:55:58 +0000 [XML-RPC] > system.multicall
2012-07-05 06:55:59 +0000 [XML-RPC] <
2012-07-05 06:55:59 +0000 Blog returned invalid data (URL: http://www.marionadie.com/blog/xmlrpc.php)
2012-07-05 06:55:59 +0000 Error syncing options: Blog returned invalid data.
2012-07-05 06:55:59 +0000 Error syncing post formats: Blog returned invalid data.
2012-07-05 06:55:59 +0000 Error syncing categories: Blog returned invalid data.
2012-07-05 06:55:59 +0000 Error syncing posts: Blog returned invalid data.
2012-07-05 06:57:02 +0000 <WordPressAppDelegate: 0x270780> applicationWillResignActive:
2012-07-05 06:57:02 +0000 <WordPressAppDelegate: 0x270780> applicationDidEnterBackground:
2012-07-05 06:57:07 +0000 <WordPressAppDelegate: 0x270780> applicationDidBecomeActive:
2012-07-05 06:58:56 +0000 <WordPressAppDelegate: 0x270780> applicationWillResignActive:
2012-07-05 06:58:56 +0000 <WordPressAppDelegate: 0x270780> applicationDidEnterBackground:
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Thanks for any help.

I have tried setting my blog to default theme and turning off plugins but that did not seem to make any difference when I attempted to log in to the app.

2012-04-14 16:03:46 +0000 <AddSiteViewController: 0x54d9a0> checkURL http://www.euphiodesign.com/blog
2012-04-14 16:03:47 +0000 <WPDataController: 0x599750> guessXMLRPCForUrl: http://www.euphiodesign.com/blog/
2012-04-14 16:03:47 +0000 <WPDataController: 0x599750> executeXMLRPCRequest: system.listMethods http://www.euphiodesign.com/blog/xmlrpc.php
2012-04-14 16:03:47 +0000 <WPDataController: 0x599750> errorWithResponse: Error Domain=org.wordpress.iphone Code=903 "Blog returned invalid data." UserInfo=0x28a2d0 {NSLocalizedDescription=Blog returned invalid data.}

Any help would be greatly appreciated.

2012-04-09 13:30:27 +0000 <WPDataController: 0x46e340> errorWithResponse: Error Domain=org.wordpress.iphone Code=903 "Blog returned invalid data." UserInfo=0x246660 {NSLocalizedDescription=Blog returned invalid data.}