I am trying to create a case in salesforce using an API user. The informatica data synchronization job inserts a record in salesforce CASE object for a specific record type. The CASE object has a lookup field to Account object. For some accounts the record creation is successful however for some it shows below error

Error loading into target [Case] : Error received from salesforce.com. Fields []. Status code [INVALID_CROSS_REFERENCE_KEY]. Message [insufficient access rights on cross-reference id:<18 digit account id>

The API user has access to al accounts still unable to insert record for few accounts. Can someone help to identify the issue?

Validated permissions of the API user and it has read access to all accounts.