You need to delete some files ASAP. Best to have greater than 2gig of free space. Many posters to these forums state that you need much more free space: 5 gig to 10 gig or 10 percent of you hd size.
Be careful when deleting files. A lot of people have trashed their system when deleting things. Place things in trash. Reboot & run your applications. Empty trash.
Go after large files that you have created & know what they are. Do not delete small files that are in a folder you do not know what the folder is for. Anything that is less than a megabyte is a small file these days.
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This will give you a list of files and folders sorted by size. Go after things you know that are big.