COM error: MailParseMailAddress

We access the LN client through the COM API (version 5.0.5 and 6.5.2). We experience the following error, during sessions when multiple COM clients simultaneously invoke the same LN client, and attempt to send an email. We have found out that the error occurs when one of the clients attempt to send an email to recipient which doesnt exist in the name and address book, e.g. summergirl.

This is and example of the stack trace that is provided by the Windows Event log:

nnotes!MailParseMailAddress + 0x138C

nnotes!MailLookupNames + 0x1BD4

nnotes!MailNoteJitEx2 + 0x495

nnotes!MailNoteJitEx + 0x29

nlsxbe!ANNote::ANNSendNote(short,void *,unsigned short,unsigned long,short) + 0x628

nlsxbe + 0xE1F9E

Have anybody experienced this problem before?