Sharepoint custom field type

I have created a custom field type which inherits directly from SPField but when I try to add the field to a list I get the following error:

One or more field types are not installed properly. Go to the list settings page to delete these fields. at Microsoft.SharePoint.Library.SPRequestInternalClass.AddField(String bstrUrl, String bstrListName, String bstrSchemaXml, Int32 grfAdd) at Microsoft.SharePoint.Library.SPRequest.AddField(String bstrUrl, String bstrListName, String bstrSchemaXml, Int32 grfAdd)

I have looked at the log file 开发者_JS百科and there is no helpful information as to what is causing the problem and I have attached the debugger to the process and it exits after the base constructor for the field type has been called.

Does anyone know what could be going wrong from this error? Many thanks in advance.

---

Unfortunately this is a general catch-all error for many issues with custom field types. If you suddenly start to get it again, you may wish to investigate the following issues in the fldtypes...xml to begin with:

1. Unrecognised ParentType
2. Changed field type name (all existing columns will have to be recreated)
3. Not deployed correctly due to debugger false-start (I hate this one)

There are many, many other possibilities; but this is a good thing to rule out at the start.