MM,
Hmm. How were you solving the problem when you had 10-20 of these?
Anyhow, it sounds like you are generating this message when you release the demand plan to ECC.
Check your material masters in ECC. Change the material status and/or material status validity dates as necessary. There is a material status in the Basic 1 tab, and a plant-specific material status in the MRP1 tab.
Best Regards,
DB49.