Pblm With Nested Transactions

Friends,

I've a very basic doubt with Nested transactions (across procedures) in SQL Server and i guess the given below sample code illustarates my doubt well more than my words ..

I've a Proc1 like this

create procedure sp_proc1
as
begin
begin tran sp_proc1
insert into tab1 values (1,2)
exec sp_proc2 1
if <Some cdn statement>
rollback tran sp_proc1
else
commit tran sp_proc1
end

and called proc sp_proc2 is like this

create procedure sp_proc2
(
@val1 int
)
as
begin tran proc2
update tab2 set col1 = 5
IF <some cdn statement>
begin
rollback tran proc2
end
else
begin
commit tran proc2
end

The pblm is when the 1st proc is executed and when the cdn statement in the 2nd proc is sucess, then it results with the error

Failed to retreive execution plan: Cannot roll back proc2. No transaction or savepoint of that name was found.

any suggestions

--SQLPgmr