Problem while using start transaction ans commit;

Hi All,

I have a small problem in using nested transactions while working on Postgres 8.0.

Ex: I have a function A() which in turn calls functions b() and c() , if i want commit something in b or c. i have to use

start transaction read write;
-- set of sql statements and then say commit.
commit;

but this is not working it is showing the the following error near start transaction read write
" ERROR: SPI_execute_plan failed executing query "start transaction read write": SPI_ERROR_TRANSACTION ";

or

if i use only commit with out the start transaction command it throwing the runtime error
as

" ERROR: SPI_execute_plan failed executing query "commit": SPI_ERROR_TRANSACTION ";

Can any one send me an example of how to use the start transaction or how to commit an nested transaction.

Thanks in advance.

Thanks & Regards,
Sri