I've attached a few pics of the different windows relating to my saving the file.
First pic shows the plain lines I have used in the file that are causing the problems.
2nd-3rd pics show window and error when saving as an .ai file.
4th-5th pics show window and error when saving as an eps – on this one I don't know why it says it is a memory problem. Everything else on my computer runs really well – I've never had that problem before. Saving as a pdf is the same as .ai file.
I think this is now just a corrupt file. Last night I tried making new files drawing lines and I kept getting the error. This morning after restarting I cannot even open the colour version of this file as it just keeps quitting Illustrator. However I can now open other old CS3 files and save them as CS5.5 and all is ok, and I can also draw lines in a new file and it saves fine.
It's really strange – but least its working on most files now.
I don't know if any of these windows will help assess the problem – I might just have to give up on these two files.