When converting very large termbases to Excel, you may get an out of memory error. We're talking really, really large files, a million terms or so. 

See Size limits - IATE for some technical details.

Go to the Performance settings and choose large file mode. That should not only allow you to convert huge spreadsheets, is also faster.

When converting from Excel, you may get a similar error. Go to the Performance settings and choose fast mode. A new library is used that can not only handle any file sizes you can throw at it, but is also much faster.

Generally, when you have a memory error, it's worth to close all apps or even restart Windows. Sometimes that frees up extra space to allow the conversion to finish.

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