Thread:Project:Support desk/articles' content doesn't load after migration

we have migrated our site made with MediaWiki 1.21.1 from machine A:
 * Windows NT CT63778 6.1 build 7600 (Windows Server 2008 R2 Datacenter Edition) i586
 * PHP Version 5.3.10
 * MySQL 5.5.21 Community Server (GPL)

to machine B:
 * Windows NT H-5024 6.3 build 9200 (Windows Server 2012 R2 Standard Edition) i586
 * PHP Version 5.6.2
 * MySQL 5.6.21-log Community Server (GPL)

and now articles' content is gone, the site's template loads, actually everything except the content of each article. When I click on "edit", on tab "Wikitext" I see that the content is in fact there. Tab "Preview" is blank.

What could be the problem?