Common causes and fixes - Text where a number is required - Cause: a cell looks like a number but is stored as text (or has non‑printing characters). - Fix: use VALUE(cell) or NUMBERVALUE(cell, decimal_sep, group_sep) or convert with Paste Special → Values (or Text → Columns). Use TRIM() to remove extra spaces and CLEAN() to remove nonprinting characters. - Example: =A1+1 fails if A1 = " 123 ". Use =VALUE(TRIM(A1)). - Wrong argument type for a function - Cause: a function expects a range or number but got text or an incompatible type. - Fix: check function docs and correct the arguments (e.g., INDEX, MATCH, VLOOKUP). - Arithmetic with text (e.g., "5" + "2" in some contexts) - Cause: using + or - with strings that can’t be coerced. - Fix: wrap with VALUE() or convert cells to numbers. - Date/time string not recognized - Cause: a date-like text isn’t in a recognizable format. - Fix: use DATEVALUE(), TIMEVALUE(), or parse with TEXT/NUMBERVALUE or convert the cell format. - Mismatched array/range sizes - Cause: functions like MMULT, INDEX with array formulas or older array-entry require matching dimensions. - Fix: ensure ranges have compatible sizes and enter array formulas properly (or use dynamic arrays if available). - Wrong delimiter or locale issues - Cause: decimal or thousands separators mismatch your locale. - Fix: use NUMBERVALUE or correct separators. - Function-specific errors - Example: LOOKUP functions returning text where numeric operations follow — adjust type or coerce result. - Hidden characters or leading apostrophe - Fix: remove leading ' or use VALUE/CLEAN/TRIM.