Excel Page Fault

Have an excel workbook that contains 3049 rows, one worksheet. Many of the rows have merged cells.

When reaching the 3049 row and trying to add one more I get the following error message:

This program has performed an illegal operations and will be shut down.

The detail shows:
EXCEL caused an invalid page fault in module MS097.DLL at 0177:306c2481.
I cannot find any information to tell me exactly why this is happening. Help would be appreciated