I'm trying to import variants into a product and keep getting the following result. I already imported the Attribute Values, and this method worked for importing a product with less variants (around 150), but I keep getting the following error when I try to import variants into a product with around 2,000 variants:

Uncaught TypeError: Cannot read property '1' of undefined

http://sistema.elhc.info/web/content/417-62c8e0c/web.assets_backend.js:4281
Traceback:
TypeError: Cannot read property '1' of undefined
    at Object.<anonymous> (http://sistema.elhc.info/web/content/417-62c8e0c/web.assets_backend.js:4281:71)
    at Object.<anonymous> (http://sistema.elhc.info/web/content/312-f7dfa1a/web.assets_common.js:650:681)
    at fire (http://sistema.elhc.info/web/content/312-f7dfa1a/web.assets_common.js:644:299)
    at Object.fireWith [as rejectWith] (http://sistema.elhc.info/web/content/312-f7dfa1a/web.assets_common.js:649:198)
    at Object.deferred.(anonymous function) (http://sistema.elhc.info/web/content/312-f7dfa1a/web.assets_common.js:651:56)
    at fire (http://sistema.elhc.info/web/content/312-f7dfa1a/web.assets_common.js:644:299)
    at Object.fireWith [as rejectWith] (http://sistema.elhc.info/web/content/312-f7dfa1a/web.assets_common.js:649:198)
    at Object.deferred.(anonymous function) (http://sistema.elhc.info/web/content/312-f7dfa1a/web.assets_common.js:651:56)
    at fire (http://sistema.elhc.info/web/content/312-f7dfa1a/web.assets_common.js:644:299) 

    at Object.add [as fail] (http://sistema.elhc.info/web/content/312-f7dfa1a/web.assets_common.js:645:467) 

This is the CSV table I'm trying to import (with 2,000 variants instead of only 3):