I am having trouble uploading my inventory spreadsheet

You may rearrange columns but the column names must stay the same.  

There could also be a corrupted name within a column ex:  In the "Shipping Manifest" column there is an entry 342, this is not a valid file, since it is missing an allowed file extension, like .xls or .pdf.

You can always email our support desk at: support@samauctionsoftware.zendesk.com