Error Occurred

I keep getting an "error occurred" message when I open my sheets at work, although they are fine at home on the same PC. Sometimes they open and I can make a few amendments before the error occurs. Although all other Zoho apps work fine I guess it might be a problem with our network (I'm not in the IT dept and it's a school network). When I go to a1.sheet.zoho.com they seem to work fine and changes are saved - if I work on my spreadsheets there when I'm at work would they still be safe or is this not advisable?