Hi there

I had similar problem also - Qt designer (Qt v4.4.0) failed to load qwt v5.1.1 plugin compiled with mingw32 in release mode. The solution was to completely delete HKEY_CURRENT_USER\Software\Trolltech\OrganizationD efaults\Qt Plugin Cache 4.3.false\C:\Qt\plugins\designer registry key. Source: http://www.qtforum.org/article/21211...lling-qwt.html

Kind regards
Rad Radish