Microsoft Excel cannot open or save any more documents because there is not enough available memory or disk space.
Sometimes, when you try to open an Excel file from Outlook you will get that annoying message you can see in an image above. There are two possible problems here and neither of them have anything to do with memory or disk space.
The problem is in Excel’s settings (more than likely).
First, try this:
Open Excel go to Excel Options > Trust Center > Trust Center Settings > Protected View and Untick the last option where it says Enable Protected View for Outlook Attachments. You can also untick all 3 of them tick boxes if you don’t want Excel to restrict you in any way when it comes to Protected View.
The second option could happen if you are opening Excel attachments from a .pst file that resides on a network share. In that case, just save it to your desktop and open it as normal. If you get an error message then Right click on the saved file, click on Properties and uncheck the option Block and then try to open the file again.
The error message is totally generic and misleading, Microsoft could do with some technical authoring. Anyways, I hope that helps you guys