Microsoft Excel – pasting large amount of HTML data

When I paste a large amount of data into excel at times (a requirement for this project) I will get a red Z Icon and no data will paste. If I retry enough times eventually my data will get pasted. This data is largely in HTML format with some japanese characters. Can anyone tell me what this icon may indicate and how I may prevent this? (machine is running windows 2000 and excel is 2002 SP3)