[luatex] strange error message: unable to start the command lualatex -interaction=nonstopmode %.tex

[Manthos]

Dear All
I installed MiKTeX 2.9 and TeXmaker to my new laptop (win7 64-bit) and I observed the following strange bahaviour.
Every time I try to compile with luatex I get the following error
"unable to start the command lualatex -interaction=nonstopmode %.tex".
If I try to compile (the same document) with xelatex and the filename is in greek I get a similar error message

"unable to start the command xelatex -synctex=1 -interaction=nonstopmode %.tex" 
but if the filename is written in latin characters everything works fine!
PdfLatex works fine in any case.
I have exactly the same set-up (miktex - texmaker - win7) to my desktop where everything works smoothly therefore I assume that an update, to either a MiKTeX package or to Texmaker, causes the problem.
Does anybody have any idea on how to fix this problem? I have already contacted MiKTeX and TeXmaker authors however I haven't received any response, yet. 
Thanks in advance! 
Manthos VogiatzoglouPhD in financial econometricsUniversity of Macedonia
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