SQL Procedure working when run manually, not running from sql server agent

Question

I have a procedure that runs fine using the execute command in SSMS, however putting the same command in a job gives the following error.
line 9, character 9, unexpected end of input
The code takes a very long XML string in UTF-8 encoding and puts it into a single nvarchar(max) cell. Then puts this string into a XML cell in a different table, allowing me to query the individual parts of the XML code using the nodes function. I cannot put
the data directly into a nvarchar cell due to encoding differences.
I can't reproduce the string here as it is very very long.
I'm just looking for ideas really as to where it might be going wrong.
Here is what I know so far:
The procedure runs without issue when executed manually
I have checked permission issues, and that doesn't seem to be the problem. The agent runs under my own account and I am a sysadmin on the database
I split the procedure into seperate parts to locate exactly where the problem is occuring. Once again the seperate procedures run fine when executed manually but an error occurs when run through SQL Server agent.
When the query is run seperately through SQL Server Agent it gives a slightly different error. This leads me to believe it is an encoding issue. However I am getting the XML from a webpage and I can't change the encoding on the webpage.
line 1, character 38, unable to switch the encoding
I know this is a long shot since you can't replicate the issue but if anyone could give an idea as to where to start looking for an answer, it would be greatly appreciated.

Answer 1

Here's how I'm taking the XML data and putting it into an nvarchar(max) column (Column Name TEXT):
Select @url = 'http://....'
EXEC @hr=sp_OACreate 'WinHttp.WinHttpRequest.5.1',@win OUT
IF @hr <> 0 EXEC sp_OAGetErrorInfo @win
EXEC @hr=sp_OAMethod @win, 'Open',NULL,'GET',@url,'false'
IF @hr <> 0 EXEC sp_OAGetErrorInfo @win
EXEC @hr=sp_OAMethod @win,'Send'
IF @hr <> 0 EXEC sp_OAGetErrorInfo @win
INSERT #TextData(TEXT)
EXEC @hr=sp_OAGetProperty @win,'ResponseText'
IF @hr <> 0 EXEC sp_OAGetErrorInfo @win
EXEC @hr=sp_OADestroy @win
IF @hr <> 0 EXEC sp_OAGetErrorInfo @win