.ics file too complicated?

[Bytheseaside]

I've just switched my mobile to EE. May this be the reason I can no longer connect to phone to the computer with BirdieSync? To get round this I tried saving the calendar as a .ics file & import it into a different calendar. I got response saying something about how it couldn't cope with multiple events in one ics file! Admittedly my calendar is pretty crowded: I use it as a detailed diary. I tried doing the "sync your Thunderbird calendar with Google Calendar, but all I got was the few Google entries were copied to Thunderbird, but not the other way round! In the course of all this, the calendar on my phone lost all it's entries!! Disaster. Luckily the computer data is still there, & saved as an ics file. Would it load back into Thunderbird if I lost the data there? The main trouble is I rely on my mobile diary to keep track of my life. Without it, I'm lost! Help please.