If, when you select an asset in the asset browser the items to perform actions on the asset (such as adding income) are unavailable or "greyed-out" then the asset is set as a "non-estate asset".
All assets recorded in Probate Plus are grouped into categories. And these categories are either those forming part of the estate value (eg a bank account), or those that do not but are included in Probate Plus for information purposes (eg settled property). So, if you're trying to add income to an asset that's been entered as having a category of not forming part of estate values then you won't succeed as the actions are disabled.
You can either - change the category of the asset to one that forms part of estate values, or go to 'File...Options...Configure system' and find the asset category in the 'List management' section. If the category should form part of estate values then place a tick in the box beside the asset category name.
NOTE : Changing the forming/not forming part of estate values setting for an asset category can have unwanted side effects. If you're unsure of what to do then please contact the help desk or your Probate Plus administrator.