Why I obtain this error trying to compile this wallet? I am not yet a Linux guy and I am going crazy trying to install the MJ Coin wallet compiling it on Ubuntu 14.04.

This are the only provided instruction to install it:


  Debian
  
  First, make sure that the required packages for Qt5 development of
  your distribution are installed, for Debian and Ubuntu these are:


apt-get install qt5-default qt5-qmake qtbase5-dev-tools qttools5-dev-tools \
    build-essential libboost-dev libboost-system-dev \
    libboost-filesystem-dev libboost-program-options-dev libboost-thread-dev \
    libssl-dev libdb++-dev


then execute the following:

qmake
make


So I have installed the dependencies using apt-get and it seems to me that I have no problem.

Then I perform qmake and I obtain the following output:

andrea@andrea-virtual-machine:~/Documenti/wallet/MJcoin$ sudo qmake
Project MESSAGE: Building with UPNP support Removed plural forms as
the target language has less forms. If this sounds wrong, possibly the
target language is not set or recognized. Removed plural forms as the
target language has less forms. If this sounds wrong, possibly the
target language is not set or recognized. Removed plural forms as the
target language has less forms. If this sounds wrong, possibly the
target language is not set or recognized.
andrea@andrea-virtual-machine:~/Documenti/wallet/MJcoin$


Finally I execute the make compile command but I obtain the following error message:

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cd /home/andrea/Documenti/wallet/MJcoin; /bin/sh share/genbuild.sh
/home/andrea/Documenti/wallet/MJcoin/build/build.h g++ -c -m64 -pipe
-fstack-protector-all --param ssp-buffer-size=1 -O2 -D_REENTRANT -fdiagnostics-show-option -Wall -Wextra -Wno-ignored-qualifiers -Wformat -Wformat-security -Wno-unused-parameter -Wstack-protector -fPIE -DQT_GUI -DBOOST_THREAD_USE_LIB -DBOOST_SPIRIT_THREADSAFE -DQT_DISABLE_DEPRECATED_BEFORE=0 -DUSE_UPNP=1 -DSTATICLIB -DHAVE_BUILD_INFO -DLINUX -DQT_NO_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I/usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++-64 -Isrc -Isrc/json -Isrc/qt -Isrc/leveldb/include -Isrc/leveldb/helpers -I/usr/include/qt5 -I/usr/include/qt5/QtWidgets -I/usr/include/qt5/QtGui -I/usr/include/qt5/QtCore -Ibuild -Ibuild -o build/net.o src/net.cpp src/net.cpp:19:32: fatal error:
miniupnpc/miniwget.h: File o directory non esistente  #include
&lt;miniupnpc/miniwget.h&gt;
                                ^ compilation terminated. make: *** [build/net.o] Errore 1


The enghlish translation of the error output is: File or directory don't exit #include miniupnpc/miniwget.h

What could be the problem? How can I try to fix it?
Like it says, you are missing the header file miniupnpc/miniwget.h.  Usually this means there is a required library that is not installed.

Ubuntu has the convenient tool apt-file for finding which package provides a particular file.  Install the apt-file package (apt-get install apt-file) and run apt-file update to install the file list.  Then you can do

$ apt-file search miniwget.h
libminiupnpc-dev: /usr/include/miniupnpc/miniwget.h


So you need to install the libminiupnpc-dev package.

Since the documentation doesn't seem to mention this dependency, you may want to report this as a documentation bug to the MJcoin developers.