SharePoint Web Parts don't work with "Incorrect properties format" error

Issue: Sometimes, when you open SharePoint 2007 site, you see that all web parts show

"Web Part Error: One of the properties of the Web Part has an incorrect format. Windows SharePoint Services cannot deserialize the Web Part. Check the format of the properties and try again."

Furthermore, sometimes this site and its web part work correctly: you see all web part working. This behavior doesn't dependent from browser version or host. You're just clicking "Refresh" and see different results: web parts work or don't work.

Possible reason: If you have more than 1 SharePoint front-end on the target farm, check, please, how do they work. If some of front-ends have problem with free disk space, you can observe problems with web part functionality. Eventlog on this front-end contains errors with ASP .NET 2.0 problems during the page generation.

During the "Refresh" in browser you can get results from different front-ends, it depends from your SharePoint load-balancing infrastructure. So you can see correct pages from "good" front-end and bad pages from "unhealthy" SharePoint front-end.

Issue is absent after disk cleanup on the "unhealthy" SharePoint front-end.