Typically, this error message is caused by a date being entered incorrectly in a date text field from Concur that is mapped to a date field in Intacct.
You can use a conditional statement in the date field mapping in Intacct to get around this by having it say "if the date being populated is __, then put this date __ instead".
For example, if ap_datecreated is mapped to Custom1, and the date entered in Concur was 01/222/18, clearly the "222" needs to be corrected. The conditional statement that you can use would be: Custom1?01/222/18:'01/22/18'|:Custom1. This statement says "if Custom1 is 01/222/18, then put 01/22/18 instead, otherwise, put whatever is in Custom1.
Value transformations will not work in this instance, because the error message is occurring during the field mapping stage and therefore it fails out before it even looks at the VT's.