I don't see why you need to access the sequence yourself as LLBLGen Pro should do that for you.
LLBLGen Pro will Query for the NEXTVAL of the serquence before inserting a new row, or if you have a trigger based sequences, the you should check the below qouted part of the docs.
Trigger based sequence values (Oracle/Firebird)
Some Oracle schemas or Firebird databases use triggers to set the sequence value when a record is inserted. LLBLGen Pro's generated code for Oracle or Firebird uses a second query to first determine the next value of the sequence (using NEXTVAL on Oracle, using 1 instead of 0 in GEN_ID on Firebird), then pass that value to the insert query as a normal value. If that code is then used to insert a row in a table with a trigger for sequence values, the trigger will update the inserted value with a new value, making the value returned to the LLBLGen Pro runtime core not the value the trigger inserted into the sequenced field. To overcome this, the Oracle and Firebird Dynamic Query Engines (DQE) can be configured to execute a sequence retrieval query which checks for the current value (using CURRVAL on Oracle, using 0 instead of 1 in GEN_ID on Firebird) after the insert took place, instead of the sequence retrieval query which checks for the next value before the insert takes place.
To do that, add the following tag to the configuration's appSettings section:
Oracle Firebird <add key="OracleTriggerSequences" value="true" />
<add key="FirebirdTriggerSequences" value="true" />
A value of false or omitting the tag will cause normal behavior, a sequence call which asks for the next value before the insert.
Either way you should make sure the correct sequence is set for the correct field in the LLBLGen Pro Designer.