file conversion ?

[coltheplumb]

Hi all , i use a common drive shared portal based at work ,this has been fine since starting to use it a few years ago but for about 6 weeks for some reason when i try and get into it i get the following message.

"The file you are trying to open works excel XLSX is in a different format than specified by the file extension. Verify that the file is not corrupted and is from a trusted source before opening the file. Do you want to open the file now?"

so i say yes but it still doesnt or cant convert the file? i have checked with my work place and they tell me nothing has been changed their end?? so any ideas guys ?
Colin xx