May be the logs can help in this to undersatnd the exact issue. But check if this is happening only for a specific class where you are trying to create data type or with specific name of the Data type.
Solution provided here is a bad one. We can't add BLOB in any external table just like that! If that is the case then why even pega is not using these columns in external tables used in pega application? Pega Engineering team needs to come up with a proper solution for this issue.
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