MS EXCEL (Office XP)

In a work book i have five worksheets containing data and in each worksheet there are nine charts.
Also there is another worksheet that has data that is linked from the first five worksheets. While making the charts in the worksheets an error is generated ” NO NEW FONTS CAN BE ADDED IN THIS WORKBOOK” while changing the titles using the chart options.Als the wokbook closes and auto saves and generates recovered files.
Also thre is a message that excel has encountered a problem. Asking for permission to send error report or not.
Never come across this error before. The file size is a mere 522 KB.
Worked with bigger files containing more no of charts .
Please suggest what I do in this case