Add info about possible plugin registration error

Readme.md

@@ -29,4 +29,19 @@ Decide whether to install the functions globally or as part of a package
 - stress test for leakage
 
 
-(TODO)
+### When things go wrong
+
+#### Errors when registering a function
+
+```
+Invalid index 1 in function IMetadataBuilder::setType
+```
+
+This error indicates that the parameters in the sql function declaration do not match the parameters in the actual function. Check your sql with the FB_UDR_MESSAGE declarations.
+
+
+
+
+
+
+### TODO