I used the "Import Spreadsheet" command in SharePointfor the first time this week, and got the following error after going through the steps of naming the list, browsing to the spreadsheet, and selecting a range:
Method 'Post' of object 'IOWSPostData' failed
I then tried exporting the list from the Excel side, and was also not successful. I'm running Office 2007, MOSS 2007, and Vista. What ended up fixing this for me was to repair MS Office via the Control Panel / Programs and Features function. At first I tried modifying the the Excel Add-In EXPTOOWS.XLA as described in this forum:
It worked (I used lver=3 and commented out the previous line), but I wasn't able to save the file, which meant I'd have to modify that piece of code every time I wanted to upload a spreadsheet. Happily, a repair of MS Office did the trick.