No users can update a particular Change Request.

When trying to update any fields user gets the following error message: 
ARERR(306) Value does not fall within the limits specified for the field : (Field ID - CHG:Infrastructure Change <10103>, Maximum length - 255)

Cause:
There is an existing defect SW00466058 regarding this, it is currently open and targeted for a future release.

Resolution:
This is related to Approval Engine utility used to extend the length of the Approval fields. The utility is able to increase the core Approval fields length to 4000, however it neglects to update one of the Change Management fields which is also responsible for holding the approval string, therefore an error occurs in Change Management. 

zTmpActingAs is not included in apchgschema utility. Need to manually increase the input length to 4000.

You need to Overlay the field (zTmpActingAs) in CHG:Infrastructure Change and set it to 4000 in order to resolve the problem.