The forum post Error on Connect Form to Salesforce seems to cover your problem:
We are rolling out the new Connect form, but are getting an error in Salesforce:
Code:
Insert failed. First exception on row 0; first error: STRING_TOO_LONG, WID: data value too large: 87b3511b-fbe1-4d03-bda6-6450a1440765
Response:
The error you are seeing is due to the instance being on an old release. The new forms use a 64 character WID and the old release had only 18 character limit on WID.
We need to update all your clients as soon as possible.
Please see the release note: Salesforce PaaS 9.7010: Compatibility Release for Connect 2
From the release notes:
WID field length increased to 40 characters for Connect 2.x forms WID.
It appears to be a mismatch between the field length in Salesforce and what the external component is expecting.