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There is no limit on the products you can upload in Magento, everything depends upon your server resources, memory limit and import tool you are using (in case you use other import method than default one).
1. If you have more than a number of products or customers, then you don’t want to spend a lot of time in creating records for them one by one.
2. You can go up with Magento Go’s Import tool, to import the details
3. With the help of the tool, you can upload a file that contains the records for as many customers or products as you want.
The error is likely to appear because of you have written something incorrectly in the CSV file. While issuing the error you will find the line number which will give you a hint what to do, please, check it.