QSQLITE : not authorized unable to fetch row - sql

Question

I'm completely stuck with loading extensions in Qt's SQLite driver. I've done all steps from this 'how to'. Just changed SQLITE_ENABLE_LOAD_EXTENSION to DSQLITE_ENABLE_LOAD_EXTENSION. After that I'm trying to run following code in my app:
QSqlQuery tSqlQuery;
QString sql_command_text;
sql_command_text = QString("SELECT load_extension(\"libspatialite-4.dll\")");
if(!tSqlQuery.exec(sql_command_text))
qDebug() << tSqlQuery.lastError().text();
And qDebug gives me this: "not authorized Unable to fetch row".
I'm using Qt 4.6.3
What am I doing wrong? I've read tons of articles but couldn't find any solution.
You can be sure in following things:
I've done all steps from how-to
I've rebuild DLLs and replaced them

Answer 1

When I face this problem I've solved it this way:
Add in Src\qtbase\src\3rdparty\sqlite\sqlite3.c next lines:
#ifndef SQLITE_ENABLE_LOAD_EXTENSION
# define SQLITE_ENABLE_LOAD_EXTENSION 1
#endif
Added it somewhere near 150 line.
Removed from file Src\qtbase\src\3rdparty\sqlite.pri from DEFINES:
SQLITE_OMIT_EXTENSION
Leave it like this:
DEFINES += SQLITE_OMIT_COMPLETE SQLITE_ENABLE_FTS3 SQLITE_ENABLE_FTS3_PARENTHESIS SQLITE_ENABLE_RTREE
then cd command line (yeah, I'm at Win) to Src\qtbase\src\plugins\sqldrivers\sqlite
and execute next commands:
mingw32-make -j
mingw32-make install
flag -j makes make use all available cores for compiling, and install copy resulted dll to plugins\sqldrivers\sqlite dir (the place where all others dll's keep) of qt installation.
On linux (Ubuntu 14.10) I had to add this line in sqlite.pro before compiling:
LIBS=-ldl