fetch in embedded sql

hello,
i have written the following method for c++

bool DB::getPresentations(Presentations &pr)
{
exec sql begin declare section;
int rID;
char pre[20];
exec sql end declare section;

rID = pr.roomID;

exec sql BEGIN TRANSACTION;
exec sql DECLARE cur CURSOR FOR
SELECT Presantation
FROM Presantations
WHERE RoomID=:rID;

exec sql OPEN cur;

// here
exec sql FETCH FORWARD 1 IN cur INTO :pre;

// and here
exec sql CLOSE cur;
exec sql COMMIT TRANSACTION;
}

if i start this method i get the following error belonging to the comments
"here" and "and here" in the code above

NOTICE: current transaction is aborted, queries ignored until end of
transaction block
NOTICE: current transaction is aborted, queries ignored until end of
transaction block

if i do the begin, declare cursor and fetch statement manually in the psql
database there is no error
thanks for every answer
best regards heinrich retzlaw