I have been trying to figure this out for the last 2 days to no avail. Accessing the ribbon on some computers gives the javascript error mentioned -
Sys.ArgumentException: Cannot deserialize. The data does not correspond to valid JSON
However, some computers work fine while others do not. For a few users, I was able to rectify the issue by doing a reset on the IE settings to default. However, this fix does not work for all users with the problem. Also, on the computers that do not work, it gives the error for all users. Strange thing is that it works on Firefox on the same computer. However, for the life of me I am unable to determine what setting is causing this issue. ....
Thanks in advance,
Jake.