Large AZW3 file without DRM won't convert

Hey there. I'm a first time poster. I have a 62 MB AZW3 book that I would like to read on my Ipad Air 2. I have tried to get it onto my Ipad in its current form, but it won't work. Changing the extension name to .mobi was no help. So I've turned to Calibre to try to convert it to mobi or epub. The book has no DRM, I am able to view it in the Calibre reader and I was able to transfer it to my kindle fire HD before it broke. But when I try converting it, the file stops at 47% for about 90 minutes before giving me this error message:

Flattening CSS and remapping font sizes...
Python function terminated unexpectedly
(Error Code: 1)
Traceback (most recent call last):
File "site-packages\calibre\ebooks\conversion\plumber.py", line 1153, in run
File "site-packages\calibre\ebooks\oeb\transforms\flatcss.py" , line 185, in __call__
File "site-packages\calibre\ebooks\oeb\transforms\flatcss.py" , line 264, in stylize_spine
File "site-packages\calibre\ebooks\oeb\stylizer.py", line 273, in __init__
File "site-packages\calibre\ebooks\oeb\stylizer.py", line 360, in flatten_rule
MemoryError


Can anyone tell me what is going on or suggest an alternative?