sql dts failure DBNETLIB connectionread general network error

I have this sql 2000 DTS package created years ago by the original developer. The package has been running fine for years but recently the job executing the package has been playing up for unknown reasons. The package just imports from a text file and then execute a series of stored procs that create daily temp tables, update some values , change some field types etc. All internal transact sql with no communication with another server etc.

Today the job failed and troubleshooting by exeuting individual steps in the pacakge identified a stored proc in the package as the culprit.
The error message is:
"[DBNETLIB][ConnectionRead (recv()).]General network error. Check your network documentation.".

And the stored proc is (yes, not very elegant):
ALTER  Procedure SP_LOAN_ASSET_UPDATE_START_MATURITY_DATES_3
AS
BEGIN
ALTER TABLE LOAN_ASSET
ALTER COLUMN ASSET_START_DATE SMALLDATETIME

ALTER TABLE LOAN_ASSET
ALTER COLUMN ASSET_MATURITY_DATE SMALLDATETIME

update loan_asset
set asset_purch_date = '990722'
where asset_loan_num = 40806
and asset_purch_date = '991722'

update loan_asset
set asset_purch_date = '020706'
where asset_loan_num = 138609
and asset_purch_date = '027706'

ALTER TABLE LOAN_ASSET
ALTER COLUMN ASSET_PURCH_DATE SMALLDATETIME

However when the stored proc was executed in query analyzer by the same user it executed fine.
As you can see, the sp just updates and alters the table.
The job owner executes under the sql agent proxy account which has the necessary rights.
We do not want a repeat of this failure as the job executes dailly at 5am when no one is in and is mission critical.

So my question is why would this job/package fail at this point occassionally when it has the necessary permissions but work 90% of the time?