Unreadable Content/Macros running help

Now and again when I open my .xlsm workbook it says unreadable content found. I click OK to recover the sheet and it opens fine and then I click enable content. My workbook is set so that each time it opens it runs loads of macros that checks the date and time and if it's within 1 hour of a set time it will fetch data from the web and paste it. However when the workbook opens as unreadable content and I then enable content it runs the macros regardless of the time being within the 1 hour window. Sometimes the workbook opens without an issue and then everything works fine and the macros only run within the time window. Any ideas at all to why this could be?

I've found online elsewhere someone has the same issue and he said he resolved it. He said

"There was problem in data validation as I was giving delimited string as formula and there is limit in the number of characters(255, i guess) and hence it was crashing.

so to solve this problem, I have copied the text in contigous cells and given name to cells range and that Name is given in data validation formula ."

What does this mean though in simple terms?!?

Any ideas?