Your file might have become corrupt somehow. This happens from time to time (it never happened to me but sometimes people here suffered from that plague). If you search the forum you will find a Mathcad worksheet able to be used to repair damaged regions.
I have deleted the region which threw that using a text editor and your sheet is now loading. But there is at least one region missing, so check the file carefully.
So we learn that its a good idea to make backups of multiple stages in the development of a document.