I am using LabVIEW to talk to Excel via its ActiveX interface.
For some reason after some time successfully writing to a spreadsheet I got this error when attempting
It's possible that the range object isn't being handled properly in the toolkit. If this is NI's reporting toolkit, you can possibly open the sub-vi's and place probes to troubleshoot the error. (This may have changed, though. I haven't looked at it since it was re-written.)
The Excel functions exposed in LV are variously called "automation" or its "object model". You can find information on where to locate the help for it at http://support.microsoft.com/kb/q222101/. A number of the links from that page have pretty good text code samples that can be translated into LV code if you care to do so.
Of course, NI's site has a number of Excel examples at http://www.ni.com/analysis/excel.htm
This error code means "Object Required."
It sounds like your toolkit might have a memory leak, or it is disposing of an object prematurely.