Help with MemoryError

Hi!
I keep getting Memory Error message while trying to convert large(>200mb) mobi files to any other format. It occurs almost immediately after start. And the error message is:

(Error Code: 1)
Traceback (most recent call last):
File "site.py", line 132, in main
File "site.py", line 109, in run_entry_point
File "site-packages\calibre\utils\ipc\worker.py", line 192, in main
File "site-packages\calibre\gui2\convert\gui_conversion.py", line 31, in gui_convert_override
File "site-packages\calibre\gui2\convert\gui_conversion.py", line 25, in gui_convert
File "site-packages\calibre\ebooks\conversion\plumber.py", line 1035, in run
File "site-packages\calibre\customize\conversion.py", line 241, in __call__
File "site-packages\calibre\ebooks\conversion\plugins\mobi_in put.py", line 33, in convert
File "site-packages\calibre\ebooks\mobi\reader\mobi6.py", line 73, in __init__
MemoryError

:help: