At present there's an issue when downloading the asset list is Excel format from the main asset list screen. This was caused by a Microsoft Excel Offfice Security patch KB3115262 - https://support.microsoft.com/en-us/kb/3115262 Which came out July 12, 2016.
There are two work-around:
1) Use the Excel csv download format instead
2) Update your Excel settings as follows:
To work around the issue, we had customers make a change in their Excel to allow files from the internet.
To fix: 1) Open Excel Go to File Options
2) Click Trust Center -> Trust Center Settings
3) Go to Protected View. there are 3 options that show that were all clicked
See this link for more details: http://stackoverflow.com/questions/38377796/export-html-table-to-excel-doesnt-open-in-office-2010/38382419#38382419