Word for Mac 2011 keeps crashing every time I work with a document, relatively large (50Mb), on MacBook Pro. When I work at the same document, in iMac, there is no problem. What could it be?

Perhaps the best way is to switch to Pages since Mac is offering it for free now. I doubt if Windows will solve this question in both system.

Unfortunately, the topic of this question has branched into several different questions and answers. If you are having troubles with Word please start a new question. Be sure to include the version of Word you are using, the text of any error messages and/or error logs you are receiving, and any other pertinent information you think might be helpful in troubleshooting the problem.

Perhaps the best way is to switch to Pages since Mac is offering it for free now. I doubt if Windows will solve this question in both system.

How have others been able to rid of this problem?

Lots of different recipes and shots in the dark, as you can see. In fact, this problem also exists in Windows.

Are you using Google Drive? If so, try turning it off or setting GDrive Sync off. Likewise, if you are using any Internet drive service, like DropBox or Syncplicity, try turning them off. In all likelihood, the problem resides in certain process still locking the large file when Word attempts to save it. Thus, doing a Save As ensures no one else is using it and the operation succeeds. 

I use Google Drive only for shared spreadsheets, but I do not use it as a way to back up or save the files that I'm working in. I'm strictly working from a Word Document that is saved in a folder on my Desktop. I was previously using DropBox, but since I rebuilt my HD and reinstalled Word, I decided to leave DropBox off and have not used it since the problem continued to reoccur. I tried looking through my Activity Monitor when this error message comes up, and I can't figure out what other process is trying to access my Word doc at the same time. But like the other users with this problem, it continues to create a new .tmp file after every error message.

I'm really not sure what to try next, but like others have said it gets to the point where I have to rename it every single time I save. How have others been able to rid of this problem?

Are you using Google Drive? If so, try turning it off or setting GDrive Sync off. Likewise, if you are using any Internet drive service, like DropBox or Syncplicity, try turning them off. In all likelihood, the problem resides in certain process still locking the large file when Word attempts to save it. Thus, doing a Save As ensures no one else is using it and the operation succeeds.