preventing excel from 'losing information'

[miconian]

Upon opening my workbook today, I got a messagebox alerting me that, if I wanted to open my workbook, I would have to live with losing some "records." I agreed, and when the workbook opened, a pivot table was gone. I clicked on the messagebox to get more info, and it led me to this xml file (shown in my web browser):

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?> 
- <recoveryLog xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main">
  <logFileName>error043760_01.xml</logFileName> 
  <summary>Errors were detected in file 'name of my file here'</summary> 
- <removedRecords summary="Following is a list of removed records:">
  <removedRecord>Removed Records: PivotTable report from /xl/workbook.xml part (Workbook)</removedRecord> 
  </removedRecords>
  </recoveryLog>

Here's my question. How can I keep this from happening again? The workbook in question has about 50 worksheets, about 52 pivot tables (all using the same data), five or six VBA macros, and some form objects like buttons and checkboxes. I've been adding a lot to it, and it's a rather important document. If I had to rebuild that pivot table at an inopportune time, that would be bad.

Sure, I can back it up. But I couldn't help noticing that this problem happened the morning after I added three new macros and several more form buttons. I'm worried that I'm bloating the workbook and turning it into something that is going to crash often. Are my fears unfounded? Is there a way to prevent this?

I'm talking about an .xlsm document created in Excel 2007 on Windows XP.

thanks!