I have recently installed LO 5.1.03 and then 5.1.10 and found both of them to have the same problem, namely that they refuse to open .xlsx spreadsheets that opened fine in all previous versions of LO. Everything was working fine when using LO 5.0.3 and earlier versions. It would seem a simple to fix to take a look at what changed in .xlsx handling, or simply revert to the handling of the earlier versions.
Since the ability to usefully exchange .xlsx files with collegues is important to me, if this cannot be simply fixed, then I am forced to re-install an earlier version that worked.
All comments welcome.
So, here’s an update: I dropped back to LO 5.0.5.2 and everything works as it is supposed to work. Therefore, the problem seems to have been created in the move to the 5.1 versions.