Filling a (validFrom) Date field causes an Error because of Date format "String was not recognized as a valid DateTime" (4380545)

This defect is related to the "Language for value formatting" value, which can be set in the Profile Settings in the Main Data. If you change it, for example, from English to German and back to English, you can set the valid from field in the request. 

The issue  is seen when the "Language for value formatting" is set to German.  The error seen in the API Server log is "String was not recognized as a valid DateTime"

This has been acknowledged as Product Defect #503551 

If you encounter this problem, please contact our Support team and request for hotfix #503551.