Why do I get 800A0E7C errors?

ADODB.Connection error '800a0e7c'  Parameter object is improperly defined. Inconsistent or incomplete information was provided.    ' or    ADODB.Connection error '800a0e7c'  The application has improperly defined a Parameter object.

 
You are probably neglecting to specify a size for a command object parameter, e.g.: 
 

cmd.createparameter("@varchar50", AdVarChar, adParamInput)

 
Should be: 
 

cmd.createparameter("@varchar50", AdVarChar, adParamInput, 50)

 
If you are using QueryDefs in Access, see KB #181716. 
 
If you are using Commerce Server 2000, and you may have empty VARCHAR columns, see KB #314789.