Since there still no solution found there more details what we did figured out since last post:
1. Form use partition areas to simulate multisteps
2. Inline validation is ok and form can be proceed to submitting but fails on submit
3. Debug on submitting shows that all fields are complete well
4. Form not working in Mac/Windows Safari and FF. In Chrome there is no issue
5. There is no any events placed on fields - so it's clear simple form.
6. Form submitting works well if website is put offline in joomla configuration. As website is put back to online, form submitting stop working.
7. This error appearing on different servers - did tryed hosted as own Apache server.
i will appreciate any support on this weired issue.
Thanks
Alex