Hello,

The reason for this is a bit complex, but the resolution is probably fairly easy. 

The Micro or Mu greek symbol does occasionally cause problems.  This is because there is the "proper" way to specify Mu using standard charactersets, and then there are other ways using specific fonts (wingdings etc..).  If the data this applies to comes from a lab it would be a good idea to ensure they are using the standard character (ASCII characher 181).

To resolve it go to Data Tables - zRef_Unit_Conversions and delete the existing conversion that "looks" the same. Filtering for it probably wont work for the same reasons that you have this issue (its a different version of hte same character).  Then try adding the conversion again through the Unit Check. 

This may resolve it completely.  However, if you have multiple different characters for Mu it may mean that the results with the other version of Mu now have an issue so the problem has become circular.   In this case probably delete the lab report and import again, but change the Mu values to a normal u.  You can still output it as Mu in the reports by specifying that as the output unit. 

Lastly, when editing ESdat output units to Mu probably better to copy and paste from one of the other compounds that already has the Mu rather than getting it from other sources (word etc..).

Luckily Mu seems to be the only character with this issue.

I hope this helps.

Warwick