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I could reproduce the problem now. It will be fixed in the next update.
This will be fixed in the next update.
Hi, the FTP server sends this error message:

550 page_01a.htm: Permission denied 

So it looks like the user you used to login doesn't have permissions on the server to create or write files in this directory. Changing file permissions on the server should fix this.

Please try to enable the "Debug Log" setting and have a look at the log file.

What is the exact error message?
For syntax highlighting, there is a also a DocBook TextMate bundle you can try at https://github.com/weppos/docbook5-tmbundle

Here's how to use custom TextMate bundles with Textastic: http://www.textasticapp.com/v3/manual/lessons/How_can_I_add_my_own_syntax_definitions_and_themes.html
Did you see the following entry regarding Docbook preview?

http://feedback.textasticapp.com/topic/80566-how-can-i-preview-docbook-files-in-textastic/

Thanks for reporting this. I'll try to reproduce and fix it.
Here is the xml stylesheet processing instruction I used:

<?xml-stylesheet type="text/xsl" href="docbook-xsl-1.76.1/html/docbook.xsl" ?>
You can download the xsl stylesheets from http://sourceforge.net/projects/docbook/files/docbook-xsl/

If you want "html" output, you only need the "common", "html", "lib" directories and the "VERSION" file as you can see in the last screenshot.
You can use Textastic's preview feature with DocBook files if you copy the DocBook xsl stylesheets to Textastic and add a <?xml-stylesheet?> processing instruction: