intermittent failure of SQL string

The following code is used to get data from SageLine50:1

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80% of tries brings down the required data but on about 20% the data field remains empty. I have attached the full application in case that would help, but as you will not have access to
the database perhaps not.

The application has an Auto_Open procedure which hides the worksheets and makes the userform which contains most of the action, visible.
As this is an intermittent fault I think it is unlikely that I will be lucky enough to receive a fully finished answer. What I am hoping for are some pointers as to how I can proceed to debug the program
John

Try delete the string in red.

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Rorya
All I can say in my defence is that the On Error Resume Next was put there to catch the situation where one or both ranges were empty. This is a bit unlikely in the app when working properly but was happening a lot during this problem.
jindon
I will try your suggestion but the line as in my code came directly from the SQL string generated by MSQuery. I'll let you know how I get on
John