Calc keeps crashing every time I copy and paste a range

I am copying and pasting a range of data from a .xlsx file to another .xlsx file. The original file was .csv ; I tried Save As to a .xlsx file but it still crashes when I copy from it and paste. The data is just normal figures, currency, dates etc, not even any formulas. What could be causing this? It’s driving me crazy!
Using Libre Office version 4.2.6.3. English language.
Operating system Windows 8.1.

Please try resetting the user profile: https://wiki.documentfoundation.org/UserProfile

Thanks, I’ve tried resetting my user profile. I’m not sure yet if it has fixed the problem, as it was intermittent. Will provide more feedback later.

Still had the problem this morning, so resetting my user profile didn’t work.
Couldn’t paste ANYTHING into the file, not even a single cell copied from the same file, whether I used CTRL C and V or right clicking / copy / paste.
In desperation I deleted all the worksheets (about 9 of them) except the main one to reduce the size of the file (it was only 23MB, not huge?) - and it seemed to cure the problem! Even stranger, I then went back to the original file with all 10 worksheets in it, and it seems to work OK too…

So problem solved, but I’d be much happier if I knew what caused it in the first place. My only suspicion is a problem with date formats. I downloaded the original CSV file (that I was copying from) from my bank, and although the dates looked like dates, Calc didn’t seem to be recognising them as dates when I tried to sort on that column - it only sorted on the day dates, which ended up with months being mixed up. Changing the format to date format made no difference; I had to format a new column and copy all the dates in by hand - not something I want to do every month!

Concerning the additional complaint regarding dates:

Your “dates” are text. You can convert them to numeric values and then format them for display as you like in situ using ‘Data’ > ‘Text to Columns…’… You can achieve the same effect already when importing from csv setting the column type for the dates column appropriately.

[PS (unsolicited): Better use genuine banking sofware.]